Lecture 4-5: Design of MSMB frames + their Detailing

IN GENERAL: “DESIGN OF SUPPORT STRUCTURES“

INITIAL STEPS:

1. Someone have to create scheme of the structure, chose materials. Raw dimensions of structural member’s cross-section’s (simple not obligatory formulas) All together= PRELINIMARY DESIGN Task of an architect, C.I.

2. Loading analysis, determination of all important load combinations. combinations can be provided with not reduced and not redistributed values of internal forces More in previous lecture, following text and in practices.

3. STRUCTURAL ANALYSIS

Calculation of internal forces ( with presumption of linear solution.) Generally Task of Structural mechanics. In the previous lecture 3 two simplified techniques were explained:

For the vertical load: Cut out simple sub-frames technique.Horizontal load (wind): Special technique based on graduate release of single storeys and distribution of the internal forces according to stiffness of actual storey members.

EP

What is detailing? Detailing is a sum of arbitrary rules and recommended rules about members dimension and primarily about arrangement of a reinforcement in a structure/member.

Detailing of MBMS frames

Basic rules you should know/understand from BL001 subject: it is e.g. reinforcement cover, anchoring length, minimal and maximal allowed distances between parallel rods for bearing and constructive bars etc. By MBMS frames we share on: Detailing of primary beam. Detailing of columns. Detailing of joints.

On following two slides are presented (only for memory refreshing) basic detailing rules. You have to know that they exist an apply them correctly if necessary, only. You will learn several new rules belonging to a different members of MSMB frames.

E

Detailing I. incorporated fromBL001 subject.

PP

EP

Summary or reinorcement detailing in RC membersDetailing I. Summary or reinforcement detailing in RC members EP

EP Spacers - donutsPrior to concreting rfcmt. should be supported in shuttering by spacers/donuts=circular spacer.

DESIGN ITSELF

Division into separate members and finding the most stressed cross-sections

Frame: divides into cross-beams (primary beams), columns, joints and footings.

E

Member = Crossbeam

Basically has roughly character of a continuous beam, it is stressed with M and V (axial forces N in the cross-beams are ussually neglected).

Design of crossbeam member is provided for extreme values of M (+/-)To be cost-effective, curtailment of longitudinal rfcmt is frequently used.

Design, detailing

Typical shape of M diagram in MSMB frame crossbeam opposite to running beam there is a bending moment difference in supports

E

Typical D M

To spare reinforcement and improve economy of an actual structure „ Curtailment“of the main (longitudinal) reinforcement is provided in the suitable cross –sections of the member/ beam.

EP

Cross- beam: The way of stressing

E

Cross beam is reinforced generally as running beam, e.g. the rfcmt. is placet to the margin with fibres in tension.

Basic parameters and shapes of a cross-beam

Rfcmt consists of main (longitudinal) rebars with possible bent-ups (not obligatory)and stirrups (links), which are by EC obligatory. Basic rules for rfcmt:

Main f 12-25 (28) mm, stirrups f 6-10 mm + stirrup hangers f 10 – 12 – 14 mm

Cross-beam is rectangle, usually. It is relatively huge, the height h should be (1/10-1/12). L Where:L is the greatest span of used bays (If there are not equal).Usually lays h in the interval [400, 800] mmThe breath b is usually in the interval [0,6; 1,0].hDon’t forget you must arrange a lot of steel bars inside!Sometime is shape of CS presumed to be „T“ beam.

Cross-beam is usually taken as rectangle or T-sectionp

RFCMT consists of main (longitudinal) rebars with possible bent-ups (not obligatory) and stirrups (links), which are by EC obligatory.

Main f 12-25 (28) mm, single stirrups f 6-10 mm + stirrup hangers f 10 – 12 mm

Space for concreting

E+EPDetailing of cross-beam according to Eurocode 1992-1-1).

(Over)lapping length lO is commonly multiple of anchoring length Lbd

lo= a6 . Lbd

a6 is coefficient of lapping, with values in the range of 1,0 to 1,5; according to the kind of stress (compression – tension) and % of lapped bars in an actual CS.As the art of stressing is usually not fully clear (depends on each possible loading case) it is usually recommended to take a6 =1,5.

EMBMS frame construction sequence

1. Starts from footing (80 % cases=pad)+ the rfcmt is extended out of the pad forlO=60d of used rfcmt.

The most important fact on this sequence is reinforcement detailing!

EMBMS frame construction seqenceI II.

2. StepTo the over-hanged rfcmt. from pad is added (wired) rfcmt of the 1st floor.Length of the rfcmt is for one storey + overhanging for lo.3. StepShattering is added and rfcmt. of the first floor horizontal spanning structures is aded, too.The columns in the 1st floor are filled with concrete together with 1st. floor structure.4. StepTo the over-hanged rfcmt. from 1st floor is added (wired) column rfcmt of the 2nd floor. And step 3. is repeated „in blue“.For more see educative video 1.

Primary’s beam possible layout of longitudinal reinforcement:(a) Without bent-ups(b) With bent-ups

(c) According to EC2 links should be used, too. (both cases)

Anchoring looksunderestimated or not solved.

EP+Cross-beam= IT1

Snímek 14

IT1 Ivo Terzijski; 16.03.2020

Primary beam detailing according to ACI code, earthquake territories

EP

Actual trend of detailing of frame

members = fear of plas�c hinges→

and fear of bad detail influence→In negative M region

ACI territory is more earthquake active :-)

Change the side with lock (by PB) or rotate the lock around the column

Open Journal of Civil Engineering

Illustrative member 1

TT

Illustrative member 2

TASK:Find 3 conceptual differences between two figured primary beams.Help: difference 1: The left beam is defactobonded armour only placed in the formwork(shattering). Watch spacers!

COLUMNSDesign and detailing

Columns designDesign is for combined action of M + N. By review an ID (interaction diagram) is frequently used.

Attention!Columns are compressive members must be taken in account:Influence of - Geometrical

imperfections- 2nd order effect if the

member is slender/long

Direct static calculation is used for design of longitudinal bars.Stirrups must respect relevant set of detailing rules, only.

Compressive part of ID, only

See educative video EV1 and EV2 Download from :https://www.edisk.cz/stahni/47923/education_videoe1_frame_bld__seq.mp4_63.96MB.html/https://www.edisk.cz/stahni/09823/education_videoe2_rfc_wired.mp4_148.97MB.html/

Follows examples of reinforcement detailing according to 1992-1-1 and alternative solutions - mostly according to ACI 11 line. Keep on mind please, that significant parts of regions covered by ACI/I11 code are earthquake areas! Unlike to Eurocodes the earthquake problems are not separated in special sub-code, there.

Such green text in following figures and photos is the latest lecturer’s comment.

Especially EV1 is very important for understanding the subject matter.

The end of part 1