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Cyprus International UniversityCivil Engineering Department

CVL548 HIGH RISE BUILDING

Title : Rigid Frame systems Submitted to : Dr. Alireza Rezaei

By Group 1 : Ali Ezreg ID :20153333 ID :20153680 Muftah Aljoat

ID :20153312 Adel Milad

May/2016

Outline History Introduction What is a Rigid Frame system? Applications of Rigid Frame system Material Properties How is Connect the Rigid Frame system? Considerations of Rigid Frame Design Behavior of rigid frames under Lateral loads Methods of Rigid Frame Design Advantages disadvantages Environment and Health Safety Case Study Conclusion

A tall building boom in the late 1920s and early 1930s in urban centers

Chicago and New York .

In the 1960s and 1970s, Professor Egor Popov at the University of

California at Berkeley and other researchers began to perform cyclic

laboratory testing of steel moment framing.

As a result of the apparent high performance of these structures, the

building codes from the 1960s adopted preferential design criteria for

steel moment frames.

Historic Development

Cont …

Fig 1: Fracturing of the column at welded beam-to-column connection in Northridge

earthquake.

In the aftermath of the 1994

Northridge, California

earthquake, damage to steel

special rigid frame connections

, spawned concern about the

reliability of established design

and construction procedures.

Rigid frame systems, also called moment frame systems, are used in steel and reinforced concrete buildings. This system consists of beams and columns .

Reinforced concrete and steel in rigid frames are used In earlier high-rise buildings, while concrete were under development, steel frames were predominated.

A rigid frame is an unbraced frame, that is capable of resisting both vertical and lateral loads by the bending of beams and columns.

Stiffness of the rigid frame is provided mainly by the bending rigidity of beams and columns that have rigid connections.

Introduction

A rigid frame system are comment system using in high rise

building in this years on the world that has more stability and less

damage due to Natural disasters like earthquake and wind load.

A rigid-frame structure is a structure made up of linear elements,

typically beams and columns, that are connected to one another

at their ends with joints that do not allow any relative rotation to

happen between the ends of the members.

What is a Rigid Frame system?

Fig 2 Rigid frame structure under construction

of Rigid Frame system ApplicationsSome examples of tall buildings using the rigid frame system with steel

structural material include:

Fig 4 The 12-storey, 55m high Home Insurance Building (Chicago,1885)

Fig 3 The 21-storey, 94m high Lever House (New York, 1952)

Cont…

Fig 5 Ingalls Building, Cincinnati, USA, 1903

The 16-storey, 65m high Ingalls Building (Ohio, USA 1903) (Figure 5)

Example of tall buildings using the rigid frame system with reinforced

concrete structural material include:

Fig 6 building height with structure form

SteelThe seismic design category AISC 341 is requires that structural steel

used in steel special moment frames meet the requirements of AISC 360 .

The specified minimum stress to be used for members in which inelastic

behavior is expected cannot exceed 50,000 psi, unless the suitability of

the material is determined by testing in accordance with AISC 341.

Material Properties

ConcreteConcrete used in composite components and in supporting

foundations must meet the requirements of ACI 318, requires a

minimum concrete compressive strength, f’c , of 3,000 psi.

Cont…

The design of a rigid frame building is not much different from

others, essentially. Considering by held together and made

stable by very tight junctions of the members (column & beam).

Similar to this, the structure of a rigid frame building is

characterized by its rigid connections of straight or tapered

columns and beams. That can be steel rigid frame or concrete

rigid frame as clarify in (fig 7).

How is Connect the Rigid Frame system?

A rigid frame derives its lateral stiffness mainly from the bending rigidity of frame members interconnected by rigid joints. The joints shall be designed in such a manner that they have adequate strength and stiffness and negligible deformation.

Modules of rigid steel frame connection

• Using angles or split tees to connect top and bottom beam flanges to columns to refuse the wind load

• By the 1960-1970, began to use the connection type as the welded unreinforced flange - bolted web, this modules couldn't refuse the lateral load

Post Northridge Special

Moment Resisting

connection (welded and

bolted) in one direction

and simple connection in

the orthogonal direction

Cont…

Considerations of Rigid Frame Design

Decrease Moment (Affects member size) Increasing Stiffness :

• Redistributes Moments • Limits Deflections

Joint Rigidity Support Types

Beam behavior (Fig 8)

Beam-to-column connections

Depending on the type of connection used,

This might trigger any of the following failure

modes:

• Fracture in or around welds.

• Fracture in highly strained base material.

• Fractures at weld access holes.

• Fracture at bolt holes.

• Shearing and tensile failure of bolts.

Cont…

Fig 8: Typical local buckling of beam flanges and web in zone of plastic hinging at high

levels of inelastic rotation.

Joint panel zone behavior

Column behavior (Fig 9).

Column splices

Column bases

Side sway Collapse

Structure P-delta Effects

Cont…

Fig 9: Formation of a single story frame mechanism, also called a "weak story"

mechanism.

The sizes of many columns also are drift-controlled because the strong-column/weak-beam provisions discussed earlier demand larger columns if larger beams are used.

Exceptions are end columns in steel special rigid frames, which often have high axial load demands and in most cases are controlled by strength design criteria.

when designed for strength considerations only, the biggest disadvantage in rigid frame systems is the size of lateral drift, which causes discomfort to residents and damage to non-structural elements.

Design Consideration - Drift

1) The first is the deformation due

to cantilever bending of the

building (bending deformation),

which is approximately 20 per

cent of the total lateral drift

(Figure 10 a).

Cont…

There are two causes of lateral drift:

Fig 10 Lateral drift in rigid frame systems

2) The second is that of the deformation

due to bending of the beams and

columns (shear deformation),

approximately 65% is due to the

bending of the beams, and 15% to the

columns, totaling approximately 80 %

of the total lateral drift (Figure 10 b).

Cont…

Fig 10 Lateral drift in rigid frame systems

The drifts of rigid, comparison with others

From the structural design point of view, tall (high-rise) buildings, because of their

unusual height, show a greater sensitivity to wind and earthquake induced lateral

loads than low-rise buildings. Estimating those lateral loads which play an important

role in the design of tall buildings is more difficult than estimating vertical loads.

Earthquake loads increase according to the building weight, and wind loads increase

according to the building height. For this reason, wind loads, while they are generally

an unimportant issue in the design of structural systems for low- and mid-rise

buildings, play a decisive role in that of tall buildings, and can even be a cause of

large lateral drift (sway) that is more critical than that from earthquake loads.

Behavior of rigid frames under Lateral loads

Fig 11: Differences between hinged frame and rigid frame structure.

Fig 12: Differences between post & beam structure and rigid-frame structure

The deflection of rigid, comparison with others

Distribution of moment on the rigid and hinged frame

• Decrease the axial load on the column, gives smaller cross section of column

• Increase the buckling at column

• Small deflection at beams • Resists lateral deformation

• More drift • Increase the axial load on

the column, gives large cross section of column

• Increase the buckling at column

Rigid frames are used when the architectural

design will not allow a braced frame to be

used. This type of lateral resisting system

generally does not have the initial cost

savings as a braced frame system but may

be better suited for specific types of

buildings.

Figures 13 & 14 show a floor plan and

building line elevation of a rigid frame system.

Methods of Rigid Frame Design

Fig 13 : Typical floor plan with rigid frames

Figure 13 indicates the solid triangle

designation typically used to show rigid

connections between beam and column

as well as girder and column.

The building elevation shown in Figure 14

indicates the same solid triangular symbols

at the floor line beam to column joints.

Cont …

Fig 14: Rigid frame building elevation

Connections between the beam and column typically consist of a shear

connection for the gravity loads on the member in combination with a field

welded flange to column flange connection. Column stiffener plates may be

required based on the forces

transferred and column size.

This type of joint is illustrated

in figure 15.

Cont …

Fig 15: Typical rigid (moment) connection

Moments get redistributed.

Deflections are smaller .

Effective column lengths are shorter .

The main advantage of rigid frame structures is that they do not have

structural walls or vertically oriented diagonal braces.

Rigid frames are provide architectural freedom in design.

rigid frames typically impose smaller forces on foundations than do

other structural systems.

Advantages of Rigid Frames

Rigid frames not specifically detailed for seismic resistance have no

special detailing criteria .

These frames are not permitted as seismic force resisting systems in

Seismic Design Categories D, E, or F .

The added cost results from the use of heavier sections in the rigid

resisting frames, requiring increased steel usage and more labor

intensive connections than is common in braced structures.

Disadvantages of Rigid Frames

The property itself can influence the design team's structural system.

Site layout and soil conditions can pose certain issues with

foundations and building geometry.

The proposed building geometry can limit the available structural

schemes due to the complexities that can result from acute angles .

Earthquake and wind impacts are always considered in choosing

frames.

Environment and Health Safety

CASE STUDY

In this study, a new lateral resistant system called hybrid frame, which is

a combination of semi-rigid and fully rigid steel connections used in 20-

story SAC frames, is presented herein : Several different patterns and locations of semi-rigid connection replacements within

the frame were examined in order to identify hybrid frames with the best seismic

performance.

The effective connection stiffness was identified by performing a parametric study on

the initial stiffness of the semi-rigid connections. Then, the cyclic behavior of the

connections with the most effective Stiffness was obtained, using nonlinear element

analysis.

Abstract Summary for the case study

The simplified model of a rigid frame

The simplified model of a hybrid frame

A rigid frame in high rise structure typically consists of parallel or orthogonally arranged bents consisting of columns and beams with moment-resistant joints.

Its unobstructed arrangement, clear of structural walls, allows freedom internally for the layout .

Rigid frames are considered economical for buildings of up to about 25 stories, above which their drift resistance is costly to control.

If, however, a rigid frame is combined with shear walls, the resulting structure is very much stiffer so that its height probability may extend up to 50 stories or more.

Conclusion

Tall Buildings: structural systems and aerodynamic Form Journal of Constructional Steel Research ( Earthquake resistance frames

with combination of rigid and semi-rigid connections )ACI (2008). Building code requirements for structural concrete (ACI 318-08) and commentary, American Concrete Institute, Farmington Hills.

AISC (2006). Seismic design manual, American Institute of Steel Construction, Inc., Chicago, IL.

AISC (2005a), ANSI/AISC 341-05. Seismic provisions for structural steel buildings, American Institute of Steel Construction, Inc., Chicago.

AISC (2006). Seismic design manual, American Institute of Steel Construction, Inc., Chicago, IL.

References