ICS 93.040

ROMANIAN STANDARD

STAS 1844-75

Classification index G 61 Replacing:

STAS 1844-50 and STAS 3418-52

Previous editions: 1950;1952,1975

ROAD STEEL BRIDGES Design rules

PODURI METALICE DE SOSEA Prescriptii de proiecatare

PONTS METALLIQUES ROUTIERS Prescriptions en vue de l�etablissement des projets Validation date:

1975-06-01

CONTENTS

1. General���������������������������..�. 1 2. General specifications for the design and the calculus of road steel bridges�..� 2 3. Calculus of stress�����������������������..�� 8 4. Tests�����������������������������.... 10 5. Construction specifications��������������������..�. 12 6 Compound (mixed) road steel bridges������������������ 15 7. Road steel bridges with orthotropic plate����������������.�.. 29 8. Testing and consolidation of existing bridges. Special specifications.

1 GENERAL

1.1 The design of road steel bridges and of steel light bridges is made in conformity with the specifications included in STAS 1911-75, :Railway steel bridges. Design specifications�, at an extent at which they are not in disagreement with the specifications from this standard. 1.2 This standard includes:

�specifications necessary for designing road steel bridges, steel light bridges and construction elements affected by road loads of mixed bridges as well as for bridges from localities, that bear a mixed traffic, road and railway (trams) at an extent at which they are in disagreement with or complete the specifications of STAS 1911-75;

-specifications necessary for the design of combined road steel bridges (mixed); -special specifications necessary for testing and consolidating the existing steel road super-structures.

1.3 When designing road steel bridges, there are used the provisions of the following standards too: - STAS 5626-71 Bridges. Terminology; - STAS 1545-63. Bridges for carriageways and streets. Light bridges. Actions; - STAS 3221-63 . Bridges for carriageways and streets. Type convoys and load classes; - STAS 2924-73. Road works. Bridges. Building limit sizes.

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© ASRO Entire or partial multiplication or use of this standard in any kind of publications and by any means (electronically, mechanically, photocopy, micromedia etc.) is strictly forbidden without a prior written consent of ASRO

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2. GENERAL SPECIFICATIONS FOR DESIGNING AND CALCULUS OF STEEL ROAD BRIDGES.

2.1 Actions. 2.1.1 The actions and loads are considered according to STAS 1545-63 and STAS 3221-63. 2.1.2 In case of steel road bridges, there are considered the actions from table 1. In calculations, the effective action groups are made by considering the most unfavorable action groups and positions, taking into account their simultaneous load-compatibility and the unique position of the actions, for stresses that occur simultaneously.

Table 1

No Actions

1 2 3 4

5 6 7 8 9

10 11 12 13 14

15 16 17 18 19 20 21 22 23

24

25 26 27 28 29 30

GROUP I FUNDAMENTAL a. Permanent actions The railway�s weight The resistance structure weight The pushing of earth Pre-compression forces b. long duration temporary actions. Loads caused by the weight of the objects or installations assembled on the bridge Yearly thermic oscillations Concrete of deformations in time Settlement and moving of foundations Average level hydrostatic sub-pressure c. short time temporary actions type convoy loads centrifugal force (for bridges located in curve) loads caused by people, on sidewalks force of inertia (for mobile bridges) the earth pushing caused by type convoys or other loads GROUP II FUNDAMENTAL Actions from 1�14 and short temporary actions Friction at mobile bearing blocks Vehicle brakes Daily thermic oscillations Temperature differences between the construction elements Wind pressure Water pressure and sub-pressure at minimum or maximum level Ice pressure Snow load (for mobile and covered bridges) Loads that occur at bracket-mounted super-structures or other similar actions, if they are performed for a long duration Vehicle striking against the bridge infrastructure (for vehicles that travel under the bridge) GROUP III SPECIAL Actions from 1�24 and one from the exceptional actions Vehicles striking against the bridge infrastructure (they are running under the bridge) Craft and ship striking against the abutments of bridges, over navigable water courses Earthquake force Loads generated by the transport, execution and the assembling of elements Loads caused by people crowding, on the carriageway and on sidewalks Loads generated by the destruction of fixed installations.

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2.2 Repartition of loads 2.2.1 The repartition of loads caused by the wheels and the caterpillar vehicles (STAS 3221-63) is made as follows: -in case of metallic bridge coverings, according to figure 1

-in case of reinforced concrete bridge coverings, according to fig. 2

-in case of Zores profile bridge coverings, according to fig. 3

2.2.2 The repartition of loads generated by the wheels of the caterpillar vehicles (trams, railway vehicles s. o.) is made according to figure 4, in the situation of the caterpillar�s direct leaning on a longitudinal girder.

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When leaning against railway sleepers, load P is distributed to several railway sleepers. In the absence of an exact calculus (girder placed on elastic environment), load P is distributed according to figure 5, regardless of the distance between the railway sleepers.

2.3 Coefficient of impact. 2.3.1 The coefficient of impact (ψ) is considered when calculating all the elements of the resistance structure, including the calculus of metallic abutments and of axle box pressure.

The coefficient of impact is also considered when testing the brace lift; the coefficient of impact is not considered, when calculating the position stability and deformations. 2.3.2 The coefficient of impact, that multiplies the loads transmitted by the vehicle type convoys, is in accordance with STAS 1545-63. 2.3.3 In case of orthotropic bridges, the coefficient of impact that multiplies the loads of beams and cross-pieces is at least 1.40. 2.3.4 For the elements that work together with the main resistance structure, the conventional calculus start, L, according to STAS 1545-63 is established as follows:

-for stresses generated by working with the main system, L is the span of the vertical girder; -for stresses generated by direct loads, L is the span of the direct loaded element.

2.3.5 In case of combination mixed girders, the coefficients of impact are adopted differently, for the concrete plate and for the metallic girders. 2.4 Active width. 2.4.1 The active width of the girder foundations is adopted, in the absence of an exact method, according to the provisions from subclauses 2.4.2. and 2.4.4, if there are provided solid cross-pieces, by the main girder braces.

It is recommended that a more precise calculus method should be adopted, in order to determine the active width in areas with great concentrated loads, in the brace zones and at continuous girders with great spans. 2.4.2 Active width, (ba) for girders that have cross-sections according to figure 6 is determined as follows:

-by the end articulated braces and along the consoles: baA = α b⋅ (1)

-in the girder field: baC = b⋅β (2)

-by the continuous intermediate girder braces: baR = b⋅γ (3)

where

b - is the plate�s real width, both sides of the core, according to figure 6

β, γ, ά - are coefficients, determined with diagrams from figure 7. Length li introduced in ratio x = il

b is

considered according to table 2.

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In order to determine coefficient γ, li stands for the greatest length of the adjacent spans to the considered brace.

No Static system Coefficients that calculate bba

Value li, inserted in ratio;

ilbx =

1 Simple leaned girder

li = l

2 Marginal span

li = 0.8l

3

Continuous girder

Intermediate span li = 0.6l

4 Console

li = l

a=b, but maximum 0.25l; c=0.1 l

for

Only for console�sloading

Acc

ordi

ng to

su

bcla

uses

1 or

2

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The oscillation of the active width along the girder is in conformity with table 2. If bac < baA or bac < baR is obtained

in an span, then the oscillations of the active width, inside the considered span are determined with the linear union of the values obtained for the active widths of the considered braces.

Stresses σ established in the sections, due to active width, ba, stand for maximum values above the cores of the girders.

The lowering of stress σ, in transversal direction is admitted as linear on b�s entire width, the bending of the stress diaphragm being determined from the condition of the stress equality, Na and N (fig 7�)

A is the plate�s cut. 2.4.3 In case of orthotropic plates, in order to establish the cut-stresses, at the active width of transversal girders, one admits the constant ba = b⋅β in the span and ba = b⋅α on the consoles. In order to test unit stresses, active width is reduced to b⋅α in the field and b⋅γ on the consoles.

Active widths for the longitudinal ribs of orthotropic plates are determined with table 3.

Table 3

Table 3: a; e - distances, cm δ � coefficient that is determined due to the diagram from figure 8, where A stands for the distance between

the cross-pieces, m.

Cross-section of the ortotrop plate To establish section stresses To test unit stresses

Active width, ba, cm

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2.4.4 In case of mixed combination girders, the determination of the active width, bc is made by adding width bv, to the active widths ba (established according to subclause 2.4.2 *), that results as follows:

-for haunch plates, bv shall not exceed the value corresponding to ά=45o; -for plates that lack haunches, bv is represented by the girder�s foundation.

*) In this particular case, real width, b does not include width bv.

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3 CALCULUS OF STRESSES 3.1 In order to calculate the stresses, the influence lines are represented graphically and for their loading, there are used concentrated forces or equivalent loads. 3.2. In case of bridges not provided with special devices for providing the combination, the element stress calculus is made due to the actions and loads from table 4, considered separately for each construction element and for each group of actions.

Table 4 The

action of thermal

oscillations

no

Construction elements

Group of

actions

Permanent

actions

Useful load

(convoys,

people, installati

ons)

Braking and

friction forces of the

supporting

devices

Wind pressu

re

Settlement and

foundation movement

Temperature

difference between

the construction elements

yearly

daily

One of the exceptional actions from

table 1, 25�30

I + + - - - - + 1) - -

II + + + + + 1) + 1) + 1) + 1) - 1 Main girders

III + + + + + 1) + 1) + 1) + 1) +

I + + - - - - - - - II + + - + - - - - - 2 Beams and

cross-pieces III + + - + - - - - + I + + - - - - - - -

II + + + + + 1) + 1) + + - 3 Bearing blocks

III + + + + + 1) + 1) + + +

I - - - - - - - - - II - - + + - + 2) - - - 4

Corner bracing

between the main girders III - - + + - + 2) - - +

I + + - - - - + - -

II + + + + + 1) + 1) + + - 5 Metallic abutments

III + + + + + 1) + 1) + + +

Map explanation: + action or load that is considered when calculating the element -action or load that is not considered when calculating the element 1) only for statically non-determined systems 2) only for dash panels with spans exceeding 80 m. NOTE the actions indicated in table 1, that are not included in table 4 are inserted in accordance with the provisions of subclause 2.1.2

3.3. When calculating beams, loads are distributed between close beams, considering the lever rule. 3.4. Cross-pieces that provide the transversal distribution of the loads transmitted by mobile convoys should be calculated by using the girder network theory. 3.5. Mobile loads situated up to 0.5 m from the axis of the cross-pieces are considered loads applied directly on the cross-pieces. 3.6. The main full-core girders are calculated according to the real oscillation of the inertia moments. There is set out a surrounding curve for each stress.

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3.7. When setting the bars or the over-lapped elements, the calculus length (l) of each single fillet weld as well as the total calculus weld (Σl), are in conformity with table 5.

Table 5

Weld type Set scheme Calculus length total calculus weld (Σl),

Single fillet weld

15a ≤ l ≤ 100a l = L - 2a 2 l

Single fillet weld, frontal, without craters

10a ≤ l ≤ 100a l = L - a b + 2l

Single fillet weld frontal and reversed, without

craters

l1≥ 10a l2 ≥ l1

l1 + l2 + b + b1

In which a is the thickness of the welding.

3.8. The joining and setting together of elements are calculated at the real maximum stresses from the joining sections, but at least at half of the possible stress from their section. 3.9. In case of compression bars, joining or fixations are admitted, by transmitting the stress by direct contact, if the following conditions are respected:

�the contact surface shall be normal, on the bar axis and processed so that it should provide a perfect transmission of unit stresses;

-the combining section shall not be subject to transversal forces and if there are transversal forces, they should be of maximum 1:10 from the compression axial forces that act at the same time;

-the union by contact shall be provided by joining methods that can take over stretch-stresses (highly resistant bolts, welding).

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3.10 If there occur no stretching stresses, in the direct contact combining section of compressed elements, the combining elements and means shall be calculated at aNc conventional stress, obtained by relation:

Ne = α N⋅ where

N is the maximum compression stress, in the bar; Ά is a coefficient , depending on the thinness coefficient,(λof the bar, according to table 6.

4.TESTS

4.1 The elements of road steel bridges and steel light-bridges and their structures are tested considering their: resistance, weariness, stability, elastic deformations and position stability.

4.2 The resistance and stability tests are made according to the provisions of STAS 1911-75. 4.3 The weariness, elastic deformation and position stability tests are made according to subclauses 4.4, 4.5 and 4.6. 4.4 Weariness tests. 4.4.1 Road steel bridge weariness tests are made only if there are loads from convoys traveling on rails. The elements exclusively subject to the action of road loads are not calculated at weariness.

4.4.2 Weariness tests are made according to STAS 1911-75, considering the provisions of this section. 4.4.3 Weariness tests are made only for actions belonging to group I. 4.4.4 Weariness tests, of the elements, are made due to theoretical equal unit efforts, πp and σp (fig 10), calculated for mono-axial stress states, with relations;

where

σp, πp-regular unit stress, tangential, caused by permanent loads; πp σp-regular unit stress, tangential, caused by road convoys; σp, πp-regular unit stress, tangential, caused by convoys that travel on rails

α - balance coefficient, considered : 0.5 for bridges from E and I class 0.8, for bridges from II and III class

σra πra - are regular admissible resistance and tangential to weariness, according to the steel quality and the asymmetry cycle ®, according to relations:

where

σpmin and σpmax and πpmin and πpmax are introduced with absolute values, the sign of R being calculated as follows:

-plus, for oscillating cycles

Thinness coefficient

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-minus, for alternative cycles.

4.5 Elastic deformation tests. 4.5.1 Elastic deformation tests of the resistance structures or of their parts are made separately for all the actions that can cause deformations, especially for

-permanent loads; -the effect of concrete deformation in time (contraction and slow flowing), at mixed girders with combination; -the effect of temperature oscillations; -mobile loads (vehicle convoys, provided in STAS 3221-63), without considering the dynamic action and the

influence of the centrifugal force at bridges located in a curve. The other temporary loads , of short duration are not considered but in justified cases.

4.5.2 The elastic deflection caused by the loads from calculus convoys shall not exceed l300

1where l is:

-the calculus span, for girders with a simple leaning; -the distance between related abutments, for girders with consoles and articulations, or for continuous girders.

4.5.3 The elastic deflection of the steel bridge coverings and of the ones with asphalt pavement shall not exceed

l4001

where l has the significance from subclause 4.5.2.

4.6 Position stability tests. 4.6.1 The tests of position stability shall indicate the absolute safety of dash panels, when overthrown, when being lifted from the braces or sliding from them.

4.6.2 The test of overthrowing safety is made only with steel dash panels, course up-oriented, considering the action of the forces transversal to the bridge (wind, vehicle beat against baseboards and in case of bridges located in a curve, the centrifugal force), in the loaded/not-loaded bridge situation, the worst situation. 4.6.2.1 Wind pressure is considered by generally acting horizontally and normally on the bridge�s axis.

In case of bridges situated in unfavorable places, or having special structures, there can be considered that wind has a 10o ascending leaning to the horizontal line.

When considering bridges whose surface, wind-exposed, is leaned to the vertical, there is assumed that wind acts normally on this surface. 4.6.2.2 When considering bridges loaded with convoys, the load is considered on a single lane, the vehicles being placed with the wheels stuck to the baseboard that is located opposite to the wind direction.

That lane shall be considered as loaded with empty vehicles, with a 5kN/mweight, or loaded with standardized vehicles, considering the most unfavorable situation.

The convoy load is introduced both ways, without a coefficient of impact. 4.6.2.3 The overthrowing safety test is obtained with relation:

c = 3.1≥r

s

MM

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where

c - is the overthrowing safety coefficient; Ms=Msg + Ms - the stability moment produced by the weight of the infrastructure, determined for the most unfavorable

moments (Msg), plus the stability moment, (Msp), produced by convoys under the conditions from clause 4.6.2.2;

Mr - is the overthrowing moment produced by the action of transversal forces and other forces that may cause the overthrowing. Transversal forces are considered in the situations from clause 4.6.2.1

4.6.2 The safety test when lifting or sliding from braces is made according to the provisions of STAS 1911-75.

5 CONSTRUCTION PROVISIONS

5.1 Minimum and maximum sizes. 5.1.1 The rolled steel minimum thickness shall correspond to the provisions from table 7.

Table 7

No Name of the piece Minimum thickness (mm)

1 Pieces in coffered, closed or welded profiles 6

2 Cores of rolled steel profiles 6

3 Balustrade elements, stiffening for local stability, un-covered elements 4

4 Iron aisles 7

5 Non-covered furs 2

6 Other pieces 8 5.1.2 The maximum rolled steel width shall not exceed the following values:

16 mm for bands assembled by riveting; 50 mm for bands made in OL 37 and )L 34, assembled by welding; 30 mm, for bands made in OL 52, assembled by welding. When choosing the maximum thickness values, there are considered the provisions of STAS R-8542-70

5.1.3 The minimum diameter of the riveters and bolts shall have the following values: 17 mm for resistance elements; 12 mm for secondary elements (balustrade, fillings etc.)

5.1.4 The minimum distance between 2 riveters in a joint is e1=3 d. 5.1.5 Maximum tightening lengths (ls) of the riveters are according to table 8.

Table 8

The diameter of the clapped riveter, d, mm 13 (15) 17 (19) 21 (23) 25 28 31

Maximum tightening length, l2, mm 34 45 58 72 88 106 125 157 192

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5.1.6 In case of secondary elements, made up of rolled-steel profiles, strengthening operations are performed by plates welded to the edges of the aisles, (figure 11 a) or between the cores (figure 11 b).

5.2 Runway and runway girders 5.2.1 The runway is performed without any interruption and provided with longitudinal and transversal slopes, to enable water flowing from the carriageway surface. The bridge covering stiffness shall provide a good behavior of the bridge pavement. 5.2.2 Beams are continuous, full-cored, and they are carried out from in rolled-steel elements or girders constructed by riveting or welding. It is recommended that welded sections, even for riveted bridges should be used. 5.2.2.1 Beam section is set up by considering economical elements. 5.2.2.2 Beams are interrupted at a maximum 60 m distance (30 meters, both sides of a stiff washer in horizontal profile), when they do not collaborate with the main girders. 5.2.3 Cross-pieces are full cored, by riveting or welding. Welded sections, even for riveted bridges should be used. 5.2.3.1 Cross-pieces from the end are calculated, if necessary, as rulers of the final gateways. In case of low-runway bridges, the cross-pieces shall allow the placing, under them, of a press that shall serve for the lifting of the brace-placed superstructure. 5.2.3.2 In case of high runway bridges, cross-pieces from the end are the upper bands of the transversal corner bracings. In order to provide the lifting from the brace, these corner bracings are provided with transversal bands, at their lower side. Lower bands are provided with plates fixed by counter-sunk rivets, or welded plates and their cores are stiffened. 5.2.4 The attachment of the beams to the cross-pieces is made by providing their continuity by the cross-pieces. 5.2.4.1 The lower foundation of the beams should be placed at the level of the cross-piece upper foundation. 5.3 Full-core girders 5.3.1 Full-core girder sections are usually performed in a I shape or in box shape. The box-shaped sections shall be performed so that they should provide the dyeing option or the hermetic closing, according to STAS 9407-74. 5.3.2 The full-core girder heights are established by considering economical, resistance, stability and flexibility elements. 5.3.3 When using full-core girders, double walled or with coffered section, diaphragms are provided, by the cross-piece attachment place. If there are no cross-pieces (the case of high runway bridges, loaded through the bridge covering), there are provided two diaphragms for each span. 5.3.4 The minimum core-thickness is 8 mm. Maximum thickness is established according to the area stability calculus and for sliding. Thinner cores are preferred, provided with longitudinal and transversal stiffening, to thick cores, lacking stiffening.

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5.3.5 The minimum thickness of the foundation plat band and the one of the angle aisles (for riveted girders) is 8 mm.

If the foundation is directly loaded by beam-moving vehicles (beam placed by the girder), the minimum thickness of the foundation elements is 10 mm. 5.4 Screen girders. 5.4.1 The lower limit of the spans that provide screen girders, their shape, height, as well as the screen type are established according to technical, economical, esthetical and exploiting related elements.

5.4.2 Maximum values admitted, of the thinness coefficients (min

max ilc=λ ), for screen girder bars are in

conformity with table 9. Table 9

Bar denomination stress λmax Foundations Compression 150 Diagonals Compression 150 Cross arms included in the system Compression 150

Compression 150 Cross arms not included in the system

Stretch 200 Foundations, diagonals, cross arms, included in the system stretch 200

Compression 150 Corner bracing bars, bands

Stretch 200 Compression 200 Horizontal corner bracing/transversal diagonals Stretch 200

5.4.3 In case of open bridges, the upper foundation shall not prevent pedestrian side visibility, or the visibility of people traveling by vehicles. 5.5 Bearing blocks. 5.5.1 In case of great width bridges, there are provided bearing blocks that can move both along the bridge and in transversal section. In case of pendulum abutments, spherical bearing blocks are provided. 5.5.2 Generally speaking, bearing block axes shall coincide with the axis of the main girders. 5.6 Sidewalks and balustrades. 5.6.1 The balustrades of the sidewalks situated outside villages or towns shall have a minimum 1.00 m height above the sidewalk. 5.6.2 The position of the balustrades is established according to STAS 2924-73. In case of curve-placed bridges, the distance between balustrades is modified, considering the special layout of the runway, in the curve. 5.6.3 The continuous bridge balustrades shall not prevent the free dilatation of the super-structure, under the influence of temperature oscillations. This condition shall be fulfilled also by the continuous installations located under the bridge. 5.6.4 Sidewalk minimum width and safety sidewalk width, for screen girder bridges with low runway is established according to STAS 2924-73. 5.6.5 In localities, Local Councils, considering the obtaining of an esthetic look, establish the balustrade and sidewalk sizes and structures. 5.6.6 By sidewalks and balustrades, when getting over the tram or trolley bus electric wires, there are taken safety measures against electrocution. When getting over electric railways, these safety measures are taken in agreement with the competent railway bodies.

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5.7 Protection against corrosion. 5.7.1 Construction elements that penetrate the runway shall be provided (around them) with orifices that allow fast water drain and waste evacuation. Should such construction provisions not be possible, there are taken special measures, concerning the protection of these elements, by covering them with plates that bear the corrosion effect, that can be replaced later on. 5.7.2 In case of upper passages, there are provided smoke-absorption devices, if traction is made by means of steam-locomotives.

6 COMBINATION ROAD STEEL BRIDGES (mixed) 6.1 General 6.1.1 Combination road steel bridges (mixed) are performed in steel girders that work in combination with an reinforced concrete/pre-stressed concrete plate, by providing special devices that prevent the slipping between plate and girders. 6.1.2 The adherence of concrete to the steel girders and the possible action of the rivet ends, from the upper side of the steel girder, are not considered as combination effects. 6.2 Materials. 6.2.1 The steels used for metallic construction are included in STAS 1911-75. 6.2.2 The steels used for bridge covering reinforcements, made in reinforced concrete or pre-stressed concrete, as well as their mechanical characteristics shall correspond to the provisions from table 10.

Table 10 Mechanical properties

Name Steel type Ǿ mm STAS Breaking

limit σr

daN/cm2

Flowing limit σc

daN/cm2

Longitudinal elasticity modulus

E daN/cm2

6�12 3700 2600 OB 37 14�28 3700 2400 6�14 5200 3700 PC 52 16�40 6400 3400 6�14 6000 4400

Reinforcing steel

PC 60 16�40

438/1-74

7800 4000

2100000

Steel wire for pre-stressed

concrete

SBP I SBP II 6482/2-73 See STAS

6482/2-73 0.85 rσ 2000000*)

Braids TBP 6482/4-74 See STAS 6482-74 2000000*) NOTE- in this standard, there was admitted the approximation 1 daN=1kgf, so that the resistance values, measured in daN

correspond generally to the resistance values given in kgf, in material standards. *) These values shall be verified at the execution moment.

6.2.3 Concretes used for reinforced concrete/pre-stressed concrete bridge coverings, as well as their mechanical characteristics, shall correspond to the provisions from table 11. If, by designing, the imperious character of such a resistance achievement is established, at a time interval shorter than 28 days, the values corresponding to the breaking limit, per cubes, compulsory on that date, are indicated, in the design. Table 11

Mechanical characteristics

Concrete type

Breaking limit σr

daN/cm2 min

Longitudinal elasticity modulus

E daN/cm2

Transversal elasticity modulus

E daN/cm2

Linear thermal expansion coefficient

άt

Transversal shrinkage coefficient

µ B 200 200 265000 B 300 300 315000 B 400 400 350000 B 500 500 380000 B 600 600 400000

0.4 E 0.000010 0.15

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6.3 Calculus of combination mixed girders.

6.3.1 Unit stresses in the concrete plate and in the steel girders are established separately, for each load. Unit stresses, resulting from the combination of steel girders are overlapped, in the plate, with the ones resulting from direct loads. If steel girders are not bound by cross-pieces or transversal corner-bracings, the unit stress is established by considering that the plate should provide also the transversal repartition of steel girder loads. 6.3.2 Unit stresses are determined in all the construction successive stages, for the following loads: -loads during transport, assembling and permanent partial loads;

-total permanent loads and convoy loads -shrinkage, slow flow and the temperature oscillation effect.

Unit stresses are combined, considering the provisions of subclause 2.1.2. 6.3.3 The combination of the plates solicited to bending or compression by bending is made by one of the following methods:

- combination, for taking over the stresses generated by mobile loads; - combination, for taking over the stresses generated by permanent loads or a part of them and by

mobile loads; - combination, for taking over the stresses caused by permanent/mobile loads and the ones caused by the

introduction of initial efforts into the structure. 6.3.4 The calculus of plates requested at bending or compression with bending is made by the admissible resistance method. 6.3.5 The determination of stress-state in mixed girders is made due to an ideal section (subclause 6.5.1) and according to the provisions from subclauses 6.3.6�.6.3.1.4 6.3.6 Concrete combination in wide area. 6.3.6.1 The establishment of deformations and sizes, statically not determined for the assessment of crack danger and for the calculus of combination devices at the ends of the girders, are admitted, as far as their performance is concerned, also considering the combination of the concrete from the wide area, according to subclause 6.3.6.2. 6.3.6.2 The concrete subject to stretch stresses is calculated only if the stretch unit stresses have smaller values than the ones in table 13, item 5�11 and if under the influence of all loads that permanently solicit the section - pre-compression, permanent load, shrinkage, slow flow, for instance- there is no stretching, at the upper side of the concrete plate, except for the ones produced by shrinkage and temperature variations, in the vicinity of simple girder bearing blocks. 6.3.6.2.1 The above-mentioned provisions are available for concrete wide area too (h1, figure 12), in the area of positive moments.

6.3.6.2.2 If the conditions from subclause 6.3.6.2 are not respected, the concrete from the wide area is considered to be cracked. 6.3.7 The reinforcing of concrete wide area. 6.3.7.1 If the concrete�s wide area is considered, for a calculus (6.3.6.2), the maximum stretch stress is taken over by an extra determined reinforcement, considering the admissible resistance elements from table 12.

When calculating the ideal section, there are considered both the concrete from the wide area and the extra stretched reinforcement and the pre-stressed reinforcement, if it exists. 6.3.7.2 If the concrete from the wide area is considered to be cracked (6.3.6.2.2), this is not considered, when calculating the ideal section, providing a special reinforcement that prevents the appearance of large cracks. This

STAS 1844-75

17

reinforcement shall be at least 0.1% from the concrete section, but no smaller than the minimum reinforcement from STAS 8076-68.

When calculating the ideal section, there are considered both the stretched reinforcement and the pre-stressed one, if they are attached according to subclause 6.9.1.7 and if the sliding force transmission is provided. 6.3.8 Initial stresses. 6.3.8.1 In order to prevent the appearance of stretch unit stresses in the reinforced concrete steel, to limit their values, or in order to economically size the combination mixed girders, initial stresses can be introduced, using one of the methods from 6.3.8.2�6.3.8.4. 6.3.8.2 The introduction of initial efforts by special technological means, during the assembling process: lifting or lowering continuous girder bearing blocks, the introduction of intermediate bearing blocks for simple girders. 6.3.8.3 The introduction of initial stresses by the pre-compression of the pre-tensed reinforcement plate, before or after providing the combination of concrete with steel girder. 6.3.8.4 The introduction of initial efforts by technological measures and by the pre-compression of the plate with pre-stressed reinforcements (6.3.8.2, 6.3.8.3). 6.3.8.5 The size of initial stresses is established so that it should make a total or partial pre-compression. 6.3.9 Shrinkage and slow flow. 6.3.9.1 Shrinkage and slow flow shall be considered according to STAS 8076-68. 6.3.9.2 In case of loads that permanently solicit the concrete section, unit stresses are calculated separately and their changes are established, caused by concrete slow flow. There should be made the difference between constant loads, in time and those that oscillate in time (shrinkage). 6.3.9.3 In case of combined mixed girders, there is established a single property of the slow final flow, φ, whose adoption is indicated in the centralizer of the stress calculus. 6.3.9.4 If the compressing of the plate, is made after establishing the combination between the girder and the plate, the influence of factor kr (STAS 8076-68) can be ignored, the compression being made at an at least 28 day age of the concrete. If compression is made before and if up to the establishment of the combination, free concrete shrinkage is noticed, factor kr is reduced by multiplication with 0.6. 6.3.9.5 When calculating shrinkage, for plate thickness values smaller than 16 cm, factor kdc (STAS 8076-68) is equal with 1.25, if concrete is treated so that shrinkage and slow flow should be delayed. 6.3.10 Temperature influence. 6.3.10.1 The action of yearly temperature oscillations shall be considered according to STAS 1545-63. 6.3.10.2 The temperature difference between the concrete plate and the steel girder is calculated as follows:

-for structures statically determined and for the calculus of combination links from the end bearing-block area, temperature oscillation influence is equalized to the one of a final shrinkage.

51010 −⋅=cε without reducing slow flow -for structures statically non-determined, the ±15o temperature oscillation between the upper side of the

concrete plate and the lower foundation of the steel frame is considered, the temperature oscillation being linear on the section�s height. 6.3.11 Unit efforts in assembling stages and assembling pre-stressing, up to the application of mobile loads. 6.3.11.1 Unit efforts for each assembling stage , for bearing blocks deformities, pre-compressions, etc. are overlapped with the unit stresses from the partial permanent loads that occur at the same time, considering the changes in concrete slow flow and shrinkage. 6.3.11.2 Steel admissible resistances are in conformity with STAS 1911-75 and the ones of concrete, according to tables 13 an 14. 6.3.12 Unit efforts from group I and II, when the bridge is to be built. 6.3.12.1 Maximum unit stresses, when the bridge is to be built, for the actions from groups I and II, are established according to the period when these stresses occur and according to their change, caused by slow flow and shrinkage. 6.3.13 Unit efforts from group I and II, after slow flow and shrinkage are finished. 6.3.13.1 Maximum unit stresses for actions from group I or II are calculated according to all the stress changes appeared after the ending of slow flow and shrinkage.

STAS 1844/3-75

18

6.3.14 Reductions admitted at the overlapping of stresses. 6.3.14.1 When overlapping unit stressed, in order to test concrete compressions (6.3.12), the pre-compression force may be reduced with 25%, immediately after pre-compression. 6.3.14.2 When overlapping unit efforts from the temperature difference with convoy unit stresses, there are considered the following groups:

-total mobile load and half of the temperature difference; -reduced temperature difference and mobile load as follows:

for spans exceeding 40 m, with 40%; for spans equal or exceeding 40%, with l%, where l is the simple leaned girder span and the average of the

continuous girder span. 6.4. Calculus of the reinforced concrete bridge coverings 6.4.1. Reinforced concrete bridge coverings are calculated due to the plate theory or due to the method from STAS 8076-68, considering the leaning against the steel girders that bear them: beams, cross-pieces, main girders.

After sides ratio (K), plates are considered as follows: -leaned against 2 sides, K equal or exceeding 2 -leaned against 4 sides, K is smaller than 2.

6.4.2 In the absence of a precise calculus, the establishing of sizes and reinforcement are made as follows: -for plates leaning against 2 sides, the calculus is made on a 1/3 l wide band, l being the span of the steel

girders that support it. Both sides, on the other two bands, the reinforcement�s section decreases linearly, as follows:

-up to minimum reinforcing, when the ends of the girder lean against the bearing blocks; -up to 25 % from the reinforcement of the central band, but at least the minimum reinforcing, when the

ends of the girder lean against transversal girders; -for plates that lean against 4 sides, the calculus is made both ways, according to the above-mentioned

method. 6.4.3 Reinforced concrete bridge coverings that lean against several steel girders are calculated with continuous plates, considering the provisions of 6.4.4. 6.4.4 When calculating reinforced concrete bridge coverings, there are considered the unequal arrows of the steel girders, under the action of mobile loads, if these girders are not provided at least with a corner bracing , or a transversal girder, amidst them.

In this sense, when considering plates leaning against several girders, in the absence of a precise calculus, based on network theory, the plate shall be dimensioned both in the field and in the bearing blocks, at a moment equal with the maximum moment of a simple leaned girder, whose span is equal with the distance between the axes of the close leaning steel girders.

When the distances between the axes of these frames are unequal, the bearing block moment is established for the half-sum of those spans. 6.4.5 In case of reinforced concrete bridge coverings, without combination, there is considered the friction that appears between the plate and the steel girders, caused by mobile loads, concrete time-deformations and temperature oscillations. 6.4.6 The calculus of combined reinforced concrete bridge coverings is made in accordance with the bridge covering function, as follows:

-according to the provisions of 6.4.1�6.4.5, as proper bridge covering; -according to the provisions of 6.3�., as foundation of the main girder.

Concrete admissible resistances are in conformity with tables 13 and 14. 6.5 Calculus characteristics. 6.5.1 The calculus characteristics of a combined mixed section represent the ideal area (A1) and the ideal inertia moment (Ii), calculated with relations;

where

Ao is the steel girder section; Af is the non pre-stressed reinforcement section

STAS 1844-75

19

Ap is the pre-stressed reinforcement section Ab is the section of the combined concrete plate (see 6.3.6 and 6.3.7);

n = bE

E0 where

E0 - is steel elasticity modulus, from the steel girder;

np = pE

E0 Eb is plate concrete elasticity modulus

Ep is the pre-stressed reinforcement elasticity modulus Io is the inertia moment of the steel girder, to its center of gravity ; Ib is the inertia moment of the plate to its center of gravity; a0 ; af; ap; ab �distances , according to fig. 13.

where,

Go is the steel girder gravity center Gi is the gravity center of the regular ideal section Gf is the gravity center of the regular reinforcement Gp is the gravity center of the pre-stressed reinforcement; Gb is the gravity center of the concrete plate; Bc is the active width of the plate, calculated according to subclause 2.4.4

6.6 Admissible resistances 6.6.1 The admissible resistances in the reinforcements of reinforced concrete plates are in conformity with table 12.

Table 12 Admissible resistances in the reinforcements of reinforced or

pre-stressed concrete plates daN/cm2 Reinforced steel type Group of actions

I and II Critical deformation test

(see clause 6.8.2) OB 37 1400 2200 PC� 52 1700 3400

Non pre-stressed reinforcements PC 60 2000 4000

2 11300 - 2.5 10500 - 3 9900 - 4 9400 - 5 9100 -

Wire SBP

6 8800 - 7 8200 -

6.1 10400 - 7.6 10400 - 9.1 9900 -

Pre-stressed reinforcements

BRAIDS TBP

Nominal diameter in mm

12.2 9400 - NOTE- admissible resistances from table 12 are also available for the anchorages of combined mixed girders. 6.6.2 Concrete admissible resistances in plates with partial pre-compression are according to Table 13

STA

S 18

44/3

-75

20

Uni

t stre

sses

C

oncr

ete

adm

issi

ble

resi

stan

ces i

n pl

ates

with

par

tial p

re-c

ompr

essi

on

Act

ion

grou

p I

II

Adm

issi

ble

resi

stan

ces f

or

test

s dur

ing

exec

utio

n N

o.

Den

omin

atio

n A

ctio

n th

at c

ause

s the

m a

nd

natu

re o

f the

stre

ss

Zone

whe

re th

ey a

re p

rodu

ced

Sym

bol

B

300

B

400

B

500

B

60

0 B

30

0 B

40

0 B

50

0

B

600

B

300

B

400

B

500

B

60

0

1 C

ompr

esse

d zo

ne

IIc

σ

100

120

140

150

100

120

140

150

100

120

140

150

2

By

com

bina

tion

with

m

etal

lic g

irder

s Fl

at z

one,

by

parti

al p

re-

com

pres

sion

' II

cσ

13

0 15

0 18

0 20

0 13

0 15

0 18

0 20

0 13

0 15

0 18

0 20

0

3 C

ompr

esse

d zo

ne

IIσ

11

0 13

0 15

0 16

0 11

0 13

0 15

0 16

0 11

0 13

0 15

0 16

0

4

Com

pres

sion

B

y ov

erla

ppin

g th

e st

ress

es

in th

e sa

me

sens

e, b

y co

mbi

natio

n an

d by

pla

te

bind

ing*

) In

the

corn

er fi

ber,

at a

n un

sym

met

rical

bin

ding

.

Flat

zon

e, b

y pa

rtial

pre

-co

mpr

essi

on

' IIσ

14

0 17

0 19

0 21

0 14

0 17

0 19

0 21

0 14

0 17

0 19

0 21

0

5 In

the

med

ium

fibe

r, if

it is

incl

uded

in

the

com

pres

sed

zone

. II

tσ

0

0 0

0 3

3.5

4 5

6 -

In th

e m

ediu

m fi

ber,

if it

is in

clud

ed

in th

e fla

t zon

e, w

ith p

artia

l pre

-co

mpr

essi

on.

' IIt

σ

10

11

13

15

12

14

16

18

8 9

11

12

7 In

the

side

fibe

r, if

it is

incl

uded

in

the

com

pres

sed

zone

. II

tσ

0

0 0

0 8

9 10

12

8 -

In th

e si

de fi

ber,

if it

is in

clud

ed in

th

e fla

t zon

e, w

ith p

artia

l pre

-co

mpr

essi

on.

IIt'

σ

25

28

31

35

30

35

40

45

20

23

26

28

9 -

In th

e co

rner

fibe

r at u

nsym

met

rical

bi

ndin

g, in

the

com

pres

sed

zone

. 0

IIt

σ

0 0

0 0

10

11

13

15

10

- In

the

corn

er fi

ber,

at u

nsym

met

rical

bi

ndin

g, in

the

flat z

one

with

par

tial

pre-

com

pres

sion

. 0

' IIi

σ

28

32

36

40

35

40

45

50

22

25

28

32

11

Stre

tchi

ng in

th

e co

mbi

natio

n di

rect

ion

Perm

anen

t trie

s, ex

cept

for

cont

ract

ion

and

tem

pera

ture

di

ffere

nce

clos

e to

bea

ring,

in

cas

e of

sim

ply

born

gi

rder

s.

In th

e to

p fib

er.

- 0

0 0

0 0

0 0

0 0

0 0

0

12

- In

the

side

fiber

t1

σ

28

32

36

40

35

40

45

50

28

32

36

40

13

- In

the

med

ium

fibe

r t1'

σ

- -

- -

16

19

21

24

- -

- -

14

Mai

n st

retc

hing

st

ress

es

- In

con

cret

e, w

hen

ther

e is

no

unit

stre

sses

und

erta

king

rein

forc

emen

t or

it is

con

stru

ctiv

ely

disp

osed

**).

t1''

σ

10

10.5

11

12

10

10

.5

11

12

10

10.5

11

12

STA

S 18

44-7

5

21

Uni

t stre

sses

C

oncr

ete

adm

issi

ble

resi

stan

ces i

n pl

ates

with

par

tial p

re-c

ompr

essi

on

Act

ion

grou

p I

II

Adm

issi

ble

resi

stan

ces f

or

test

s dur

ing

exec

utio

n N

o.

Den

omin

atio

n A

ctio

n th

at p

rodu

ces t

hem

an

d na

ture

of t

he st

ress

Zo

ne w

here

they

are

pro

duce

d Sy

mbo

l B

30

0 B

40

0 B

50

0

B

600

B

300

B

400

B

500

B

60

0 B

30

0 B

40

0 B

50

0

B

600

15

Lim

it va

lue

of d

etru

sion

uni

t st

ress

es to

whi

ch n

o de

trusi

on te

st is

mad

e.

- 1τ

10

10

.5

11

12

10

10.5

11

12

10

10

.5

11

12

16

Uni

t stre

sses

val

ue fo

r whi

ch

one

mak

es th

e de

trusio

n te

st

for 6

0% o

f the

det

rusi

on

forc

e.

- 2τ

10

10

.5

11

12

10

10.5

11

12

10

10

.5

11

12

17

Uni

t stre

sses

val

ue fo

r whi

ch

the

inte

gral

test

(100

%) i

s m

ade

-

3τ

17

18

20

21

17

18

20

21

17

18

20

21

18

Det

rusi

on

stre

sses

tra

nsm

itted

in

con

cret

e by

mea

ns o

f de

vice

s tha

t pr

ovid

e co

mbi

natio

n

Max

imal

det

rusi

on

adm

issi

ble

unit

stre

sses

. -

4τ

34

36

39

42

34

36

39

42

34

36

39

42

19

Rei

nfor

cem

ent

adh

eren

ce

unit

stre

sses

-

At s

moo

th b

ars

adτ

8 8.

5 9

10

8 8.

5 9

10

8 8.

5 9

10

20

Loca

l pr

essu

res o

n ca

tche

s B

ases

adm

issi

ble

stre

ss

- lt

σ

80

100

115

130

80

100

115

160

80

100

115

160

21

- W

hen

conc

rete

cov

erin

g is

m

inim

um 2

d lt'

σ

120

140

160

180

120

140

160

180

120

140

160

180

22

Con

tact

pr

essu

res o

n ba

ils a

nd

rods

-

Whe

n co

ncre

te c

over

ing

is

min

imum

5d

lt''σ

14

0 17

0 19

0 22

0 14

0 17

0 19

0 22

0 14

0 17

0 19

0 22

0

*) F

or p

late

bin

ding

in th

e no

rmal

sens

e on

the

com

bina

tion

dire

ctio

n, th

e va

lues

at i

tem

. 1 a

re ta

ken.

**

) If t

he m

ain

stre

tchi

ng u

nit s

tress

es e

xcee

d th

ese

valu

es, t

hen

a ne

w re

info

rcem

ent s

hall

be c

alcu

late

d fo

r und

erta

king

the

unit

stre

sses

and

it sh

all b

e pr

ovid

ed to

the

zone

s whe

re 0

.75

of th

ese

valu

es a

re

exce

eded

. **

*) F

or m

ain

stre

tchi

ng u

nit s

tress

es b

elon

ging

to v

alue

s sho

wn

at it

em 1

6 an

d ite

m 1

7, th

e de

trusio

n te

st is

det

erm

ined

by

linea

r int

erpo

latio

n be

twee

n 60

% a

nd 1

00%

.

STA

S 18

44/3

-75

22

6.6.

3.

Stre

tchi

ng a

dmis

sibl

e re

sist

ance

s of

conc

rete

from

tota

l pre

-stre

ssed

pla

tes,

acco

rdin

g to

tabl

e 14

. N

OTE

- Adm

issi

ble

resi

stan

ces f

rom

tabl

e 14

are

ava

ilabl

e on

ly if

they

diff

er fr

om a

dmis

sibl

e re

sist

ance

s pro

vide

d in

tabl

e 13

, for

the

sam

e un

it ef

forts

.

Tabl

e 14

U

nit e

fforts

St

retc

h ad

mis

sibl

e re

sist

ance

s of t

otal

pre

-stre

ss p

late

s G

roup

of a

ctio

ns

I II

A

dmis

sibl

e re

sist

ance

s for

test

s dur

ing

the

exec

utio

n no

D

enom

ina

tion

scop

e sy

mbo

l B

300

B

400

B

500

B

600

B

300

B

400

B

500

B

600

B

300

B

400

B

500

B

600

1 M

ediu

m fi

ber

' IIt

σ

0 0

0 0

6 7

9 10

3

3.5

4 5

2 M

argi

nal f

iber

II

tσ

0

0 0

0 15

18

21

25

8

9 11

12

3 A

t the

cor

ner,

with

obl

ique

ben

ding

0

IIt

σ

0 0

0 0

20

23

26

30

10

11

13

15

4

Stre

tch

in

the

com

bina

tion

di

rect

ion

In su

perio

r fib

er, f

or a

ll pe

rman

ent l

oad

situ

atio

ns,

exce

pt fo

r shr

inka

ge a

nd te

mpe

ratu

re d

iffer

ence

s nex

t to

the

bear

ing

bloc

ks, f

or si

mpl

e le

aned

gird

ers

0

0 0

0 0

0 0

0 0

0 0

0

5 M

ediu

m fi

ber

' 1tσ

8

8.5

9 10

8

8.5

9 10

8

8.5

9 10

6 M

argi

nal f

iber

t1

σ

16

19

21

24

20

23

26

30

16

18

21

24

7

Mai

n st

retc

h st

ress

es

In c

oncr

ete,

cal

culu

s det

erm

ined

rein

forc

emen

t is n

o lo

nger

nec

essa

ry

'' 1tσ

10

10

.5

11

12

10

10.5

11

12

10

10

.5

11

12

STAS 1844-75

23

6.6.4. The admissible resistances of steel, from metallic girders, of mixed combined bridges, as well as admissible resistances at weariness tests, are considered according to STAS 1911-75. 6.7. Devices that provide the combination between the concrete plate and the steel girders. 6.7.1 General specifications. 6.7.1.1 The devices that provide the combination shall provide the transmission of the sliding forces, that occur between the plate and the steel girders, at the combined mixed girders, for all groups of actions and in all the execution stages. 6.7.1.2 When confronted with loading cases, when less than 80% of the permanent load acts against the mixed combined girder, during the calculus of the devices necessary for providing the combination, in this particular loading case, there is added half of the permanent load, acting only against the steel girder, besides the permanent load that acts against the combined girder. 6.7.1.3 Sliding forces (Σ T), resulting from:

-temperature differences that act against the ends of the steel combined mixed girder (the concrete plate having a lower temperature than the steel girder);

-concrete shrinkage; -plate pre-compression are in general, opponent forces to sliding forces form the external loads and if a more precise calculus is not

made, they can be distributed according to figure 14, one a triangular surface (F), extended on a portion from the end of the girder, equal with:

b=bc, where bc is equal with the plate combination width.

There can be obtained, from the diagram (fig 14), stress Tx (the marked surface), corresponding to any device (dc), in order to provide the combination. To the sum of the sliding forces, (Σ T), the sliding forces resulting from permanent and mobile loads are added, at the extent at which they act in an unfavorable manner. 6.7.1.4 Girders upper foundation shall be calculated at local stresses, introduced by the combination specifications. 6.7.2 Catches 6.7.2.1 When calculating catches, to establish the contact pressure between their surface and the concrete, only the sliding force (the axial force can be ignored) is considered. 6.7.2.2 The sliding force (T), that can be transmitted to a catch is

T = A1 1σ⋅ (11) where

A1 is catch front surface:

3

11 A

Aσσ = (12)

STAS 1844/3-75

24

where,

σ is the unit stress admissible in the plate concrete, according to table 13. A is the surface that pressure is distributed on, considered;

-in haunchless plate situations (fig 15 a) A = 2d2

-in haunch plate situations (fig 15 b)

A = b1d1

The horizontally disposed dimension of surface A is limited to 10 d and 5 b1. 6.7.2.3 When calculating the weldings for the attachment of catches to the steel girders, both sliding forces (T) and the

overthrowing moment M = 2hT ⋅ , caused by T forces (fig 16), are considered.

6.7.2.4 The distances between catches are established so as to avoid the appearance of shearing forces, along the boundary of the catch range, caused by sliding forces. In case of haunch plates, the shearing force surface may be generated transversally, from the catch upper edge (t), onto the haunch (fig 17)

Theoretical point

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Establishing the distance between catches is made so that the projection of the horizontal surface, A1, of a catch, on the frontal surface of the next catch (A2), under degree α, according to figure 18, should be at least three times greater.

6.7.2.5 In case of stiff catches, concrete pressure can be distributed uniformly on the frontal sides of the catches. In case of low stiffness catches (eg: metallic profiles), the admissible pressure on the frontal sides is reduced according to the compliance possibilities of each catch component. 6.7.3 Braces. 6.7.3.1 Braces are placed so as to take over the sliding forces, by soliciting them at stretching. 6.7.3.2 Bail-shaped braces are tested at the contact pressure between bails and concrete.

This test can be ignored if: -the bails are made in rods, at least OB 37 types; -the diameter of the bails is at least 15 d (d is the concrete steel diameter, or the average of the two

dimensions of the cross section, when performing flat steel bails) -the concrete covering, on the direction of the force that drives the bail, is at least 3 d.

6.7.3.3 Sliding force, (T), that can be taken over by a brace, is determined with relation:

T = A aσ⋅ (15) where,

A is the brace section surface σa is the unit admissible stress into the brace, according to table 12.

NOTE- The sliding force is not projected in the brace direction. 6.7.3.4 Braces are leaned both senses, if the siding force can have different senses. 6.7.3.5 The sliding force can be taken over only by braces, but solid catches shall be provided, at the ends of the girders. 6.7.4 Catches with braces. 6.7.4.1 The sliding force (T), that can be braced by a brace catch, is determined with relation:

T = A1 aA σµσ 21 + (16) Where,

A1 is the catch frontal surface; σ1 is the admissible unit stress, according to table 12. µ is the adherence coefficient, with values: 0.5, for cam braces and 0.7 , for bails. A2 is the area of the brace section, on a catch. σa is the admissible unit effort, in the brace, according to table 12.

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6.7.4.2 When calculating weldings for attaching catches with steel girder braces, there are considered the stretching forces (bent) from braces. 6.7.5 Connecting rods 6.7.5.1 Sliding force (T) that can be taken over by the connecting rod, considering rod type and its diameter (d), as well as the ratio h/d, where h is the connecting rod height, can be taken from table 15, where σ b28 is plate concrete resistance, in 28 days.

Table 15 Connecting rod type d mm h/d Sliding force

Connecting rod without Cap - ≥ 5

With spiral T = 40d2 *)28bσ

Connecting rod with cap Without spiral

19�26 ≥ 4.2 T = 50d2 *)28bσ

*) d, cm σ b28, daN/cm2

6.8 Tests at mixed combined girders. 6.8.1 Crack tests. 6.8.1.1 The crack test of reinforced concrete plates, that can be used for carriageways, or having a bad water proof insulation, is made by comparing plate�s stretch stress to the admissible resistances from table13, item 5�11 and from table 14, item 1�.4.

Concrete stretching area reinforcing is made according to subclaues 6.3.7.1 6.8.1.2 The crack test of plates with special waterproof insulation is made by admitting the cracked concrete stretched area.

In order to prevent the appearance of large cracks, concrete stretches, considering the cracked section hypothesis, shall not exceed the double of the values from table 13, no 5�11 and table 14, item 1�4. The reinforcing of the stretched concrete area, is made in this situation, according to subclause 6.3.7.2.

6.8.2 Critical deformation tests. 6.8.2.1 The test is made for the next extraordinary group of actions:

-pre-compressing stress, in concrete, from the pre-stressed reinforcement; -pre-compression stresses in concrete, from the assembling technological measures (bearing block

deformities); -stresses at permanent and convoy loads, multiplied at 1.6 coefficient.

In case of systems statically not-determined, stresses caused by shrinkage are also introduced, slow flow and temperature oscillations.

Admissible resistances are: -steel flowing limit, for steel girders; -0.6 σ b28, for reinforced concrete plate; -the values from table 12, for plate reinforcement.

6.9 Construction specifications. 6.9.1 Reinforced or pre-stressed concrete plate. 6.9.1.1 The runway, for mixed combined bridges, is made by one of the following devices:

-direct traffic, on the reinforced or pre-stressed plate (without pavement and without protection or insulation layer)� this system is least recommended;

-the providing of asphalt pavements on the concrete plate (without hydro-insulation); -the providing of asphalt pavement and water-proof insulation; this system is recommended.

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6.9.1.2 Concrete plate minimum thickness is considered as indicated in table 16. Table 16

Concrete plate�s minimum thickness,cm

Bridge load class B 300

B 400 B 500 B 600

E 20 18 I 18 16

II, III, IV 16 14

When considering direct carriage plates, minimum thickness is extended with 2 cm and the covering, specified for reinforcements is extended with 1 cm, by not considering concrete wear layer thickness.

Concrete minimum type for direct carriage plates is B 500.

6.9.1.3 The leaning of the concrete plate, against girders, is made with or without haunches. Haunches shall have a minimum 1:3 minimum gradient. (fig 19).

6.9.1.4 The construction solution that is adopted shall provide the achievement of empty spaces between the plate and the steel girder, necessary for supporting. 6.9.1.5 When the pre-compression procedure is adopted before providing the combination of the plate with the girder, there is offered the possibility of the plate sliding on the girder, at the introduction of the pre-compression stress. In this particular case, there should be considered the friction forces. The contact surfaces, between the plate and the girder shall be secured against rust. Plate free movement, during pre-compression may also be assured by using roll or ball-based devices. 6.9.1.6 In case of direct carriage plates, the reinforcement corrosion should be prevented, by the areas stretched at the upper side (continuous girders). In this sense, there are provided extra-reinforcements, that are braced into concrete, in its compressed area. They can be welded to the upper foundation of the steel girders. 6.9.1.7 Concrete plate reinforcing is made according to STAS 8076-68. The plate marginal field is supplementary reinforced with a horizontal washer, to provide the taking over of the stresses caused by concrete shrinkage and by temperature oscillations, as well as their transmission to upper sides of the steel girders, by strengthening devices, placed in the end zones. 6.9.1.8 Pre-stressed reinforcements, used for pre-stressed plates are uniformly distributed on the whole plate width and braced correspondingly. When establishing stretch-stress losses, in cables, by friction, the frictions between the concrete plate and the steel girders are considered. Regular reinforcement, along the bridge, has a diameter, position and rod number established by calculus, or constructively. The maximum distance between two rods is 35 cm. The reinforcement from the negative moment area is distributed on plate combination width, established according to subclause 2.4.4 and anchored in plate�s compressed zone or welded to the girder upper foundation. The same procedure is used for the reinforcing of the non-combined plate (inactive). 6.9.1.9 When assessing concrete shrinkage, there is considered the cross-piece presence, that prevents the free slab shortening, both longitudinally and transversally to the bridge. 6.9.1.10 Plate concrete pre-compression by assembling measures or cables, is made only after reaching 80% from the concrete�s type. In order to avoid shrinkage cracks, or resulting from temperature oscillation, the bearing blocks can be lower or perform a pre-compression, in two or several steps, even before making 80% of the concrete type. In this situation, the first steps are as small as possible, to prevent fresh concrete slow flow.

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6.9.2 Combination-providing devices 6.9.2.1 When choosing the combination devices, small and frequent types are preferred (to solid, rare types). 6.9.2.2 The distance between the combination devices, disposed longitudinally to the steel girder is of maximum 3 hv, (plate thickness). 6.9.2.3 The combination devices are generally fixed by welding to the metal girder foundation. Welding quality shall be the same as the one performed at the main girder. 6.9.2.4 Types of combination devices:

-stiff catches (flat steel, angle, T, U etc.)

Braces shall be leaned at 45o to the girder foundation, their length being established so as to allow bracing to take

place in the upper side of the adherence plate and bracing adherent length should be at least 30 d, where d is the diameter of concrete steel. Brace cams are not considered, when calculating brace length. Braces are welded to the girder foundation, directly, or by bending; in the last case, bending shall be hot-processed, at a lowest angle. Brace minimum diameter (d) is d>12 mm.

Catch use, as shown in figure 21 prohibited

- braces: concrete steel, with cams, bails or hoops (fig 22)

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- catches provided with braces, obtained by combining the devices from figure 20, with the ones from figure 22. (fig 23)

-Vertical connecting rods automatically bottom welded to the steel girder foundation, provided at the upper side with a bail or a swelling. (fig 24)

7 ORTOTROP PLATE ROAD STEEL BRIDGES

7.1 General. 7.1.1 Steel bridge orthotropic plates are made in board stiffened with longitudinal ribs (beams) and transversal ribs (cross-piece, usually, of different stiffness. 7.2 Orthotropic plate calculus. 7.2.1 When calculating orthotropic plates, the function cumulating principle is applied, considering that the bridge covering, besides having a local load taking over role, is combined with the main resistance structure girders, standing for their foundation. 7.2.2 Orthotropic plate active widths are determined according to subclauses 2.4.2 and 2.4.3. 7.2.3 The admissible resistances, considered at the orthotropic plate resistance test, are established for their various functions and for the various groups of actions, according to table 17.

Table 17 Nature of unit stress to be tested Admissible resistance values for

Normal Tangential Group Group Group Orthotropic plate function σ τ I II III

Main girder foundation GPσ GPτ aIσ aIIσ aIIIσ Bridge covering, for taking over and transmission of local loads: - longitudinal of the bridge

lσ lτ aIσ aIIσ aIIIσ

- transversal of the bridge tσ tτ aIσ aIIσ aIIIσ Main girder foundation, bridge covering for taking over and transmission longitudinal to the bridge of local loads

GPσ + lσ GPτ + lτ aIIσ aIIIσ aIIIσ

Horizontal corner bracing cvσ cvτ - - - Main girder foundation, bridge covering for taking over and transmission longitudinal to the bridge of local loads and horizontal corner bracing

GPσ + lσ + cvσ GPτ + lτ + cvτ - aIIIσ aIIIσ

σech **) equivalent unit stress in board median plane

aIIσ aIIIσ aIIIσ

*) values σaI, σaII, σaIII stand for basic admissible resistances of steels, established according to STAS 1911-75. **) bending and sliding stress values in the board, under the local load actions are not considered.

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7.2.4 The eccentricity, in vertical plane, of longitudinal ribs, to board median surface and the stiffness at twist, of non-coffered longitudinal ribs, may be neglected. 7.2.5 In order to determine the stresses in longitudinal ribs, on basis of the continuous average elasticity theory, transversal ribs are considered to be discontinuous, on the longitudinal rib direction. 7.2.6 In order to determine solicitations in the transversal ribs, orthotropic plates can be solved both by according to the continuous average elasticity theory and that of girders network. 7.2.7 Orthotropic plate�s local stability and the one of other components and of the whole assembly are tested according to STAS 1911-75. 7.2.8 The wear calculus of orthotropic plate board, of other components and of the whole assembly is made in conformity with clause 4 of this standard. 7.2.9 Orthotropic plate board minimum width (t), cm, is determined by relation:

T = 2.5l 3

2EP

(17)

where, l is the distance between longitudinal ribs, cm; P is the pressure transmitted by the wheel to the contact surface, without coefficient of impact, dan/cm2 E is steel elasticity modulus, daN/cm2.

7.2.10 If the distances between longitudinal or transversal ribs are unequal, the average value of these distances is admitted, in calculation, if their difference does not exceed 20%. 7.3 Construction specifications. 7.3.1 Covering plate. 7.3.1.1 Bridge covering plate shall have a thickness that provides resistance, stability and deformation conditions. 7.3.1.2 The thickness (t) of the covering plate is:

t ≥ 25l

, but at least 12 mm

when considering light bridges and bike runways, the bridge covering plate�s thickness is:

t ≥ 40l

, but at least 10 mm

7.3.1.3 Covering plate worksite joints are made as follows:

-in case of flexible ribs, according to figure 25

figure explanation 1) factory-processed board 2) worksite-processed board, at necessary

length 3) board joint manufacturing detail 4) rewelded commissure root 5) longitudinal rib 6) cross-piece(transversal rib) 7) patching section (l=500 mm) 8)flat steel, width=30 mm and length

=900 mm, welded to the rib

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-in case of stiff ribs, according to figures 26 or 29

7.3.2 Longitudinal ribs. 7.3.2.1 Flexible longitudinal ribs are made in plat bands, T profiles, with regular symmetry axis on the board to be stiffened. 7.3.2.2 Longitudinal ribs are continuous, crossing the cross-piece spans, by windows specially designed on this purpose. At crossing, unilateral welding (fig 27 a), of longitudinal ribs is preferred, to bilateral welding (27 b), any time nature and stress amplitude allow it.

Sizes are expressed in cm Fig. 27

In case of bilateral welding, rib crossing slot has a thickness exceeding the rib thickness with 1 mm. 7.3.2.3 The distance between longitudinal ribs shall be

-max. 300 mm, in the carriageway -max. 1000 mm, outside the carriageway.

7.3.2.4 Stiff longitudinal ribs, coffer-shaped, are usually performed with a trapezoidal section (fig. 28 a). Curved joint coffered sections are avoided (fig. 28 b and 28c).

Sizes are expressed in mm

Fig. 28

figure explanation 1) factory section 2) patching section (l=section

length) 3) coffered rib joint 4) factory welding (u) 5) and 6) factory commissures

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7.3.2.5 The patching of flexible longitudinal ribs is made by inserting a worksite processed cut section, to compensate size differences (fig 25). Flexible longitudinal rib assembling joint is made by abutting joint, the piece edges being Y-shaped processed. 7.3.2.6 Coffered longitudinal stiff rib patching is made by inserting a section similar to the one provided at clause 7.3.2.5, of a 500 mm maximum length, cut on the worksite area. The joint is usually placed at the quarter ends of the longitudinal rib slots. An at least 150 mm distance between the rib joint and the covering plate joint (fig 29) is left.

Figure explanation:

1)covering plate joint; 2)support plate; 3)the attachment of the coffered rib to the cross-piece Fig.29

7.3.2.7 Coffered ribs get continuously through the cross-piece span. When windows can not be made in the cross-piece span, for construction reasons, longitudinal ribs are welded to the cross-pieces, by means of a small plate, according to fig 29. 7.3.2.8 There are provided channeled beams (1), attached to the orthotropic plate foundation (2), by a longitudinal stiffening. There is provided a protection plate, between the beam and the plate, to prevent beam movement and level possible plate deformities. (fig 30)

Beam bolt attachment is not accepted, as the beam shall be welded to the protection plate. 7.3.3 Transversal ribs. 7.3.3.1 Transversal ribs (cross-pieces) are made as T welded girders. The distance between cross-pieces is maximum 3000 mm. 7.3.3.2 Habitual cross-pieces are placed orthogonally, on the longitudinal ribs, except for the end cross-pieces from oblique bridges. The patch of cross-pieces is made similarly with the one of longitudinal flexible ribs (fig 25). Patching, devices, performed by pre-stressed highly solid bolts, can also be used, when the worksite welding is not possible.

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8 TESTING AND STRENGTHENING OF EXISTING BRIDGES SPECIAL SPECIFICATIONS

8.1 Test calculus convoy shall correspond to the load class specified for the bridges on the road where the bridge is placed. If, during the testing process, there is noticed that the bridge does not correspond to the road class, the test for a convoy, corresponding to a lower class is admitted, with the approval of the road management committee. 8.2 Mobile loads are considered according to STAS 3221-63, if the end user does not admit a special load convoy. 8.3 When testing existing bridges that are not strengthened, the coefficient of impact is calculated with relation:

L++=

5.37151φ

where, L has the significance provided in STAS 1545-63. 8.4 When consolidating bridges, size improvements are considered, according to STAS 2924-73, taking construction measures, such as removing sidewalks or a part of the carriage bridge covering (console), in case of up-oriented runway bridges. Vertical size respecting stands compulsory.

_______________

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Elaborated by: Ministry of Transports and Telecommunications

Institute of Auto, Naval and Air Transport Design, in collaboration with the Institute of Constructions from Bucharest - Bridges Department Project coordinators: From I.C.B.-C.P.

- Eng. Andrei Caracostea, Ph.D., - Eng. Iulian Alexiu, Lecturer, - Eng. Edgar Buiu, Lecturer.

From I.P.T.A.N.A. - Eng. Doru Iosif, - Eng. Dan Romascanu

Edited by: Romanian Standards Institute, Constructions and Building Materials Department,

Eng. Camelia Savescu

Collaborators: - Polytechnic Institute, Timisoara; - Polytechnic Institute, Iasi; - Polytechnic Institute, Cluj; - Ministry of Industrial Constructions; - Hunedoara Industrial Station; - Timisora Welding and ware Tests Station; - Institute of Metallurgical Researches; - Institute of Construction Researches and Construction

Economy (INCERC); - Institute of Researches and Design for Wood Industry

(ICPIL); - Institute of Studies and Design for Land Improvements

(ISPIF); - Institute of Railways Design (IPCF); - Roads and Bridges Construction Enterprise � Bucharest; - Railways Constructions Station; - Metallic Bridges and Concrete Prefabs Enterprise � Pitesti.