B.TECH FINAL YEAR PROJECT REPORT

PROGRESSIVE COLLAPSE ANALYSIS OF AN

RC STRUCTURE

UNDER GUIDANCE OF SUBMITTED BY

DR. GOPI KRISHNA , S.SOUMYA RANI 121256

ASSISTANT PROFESSOR K.N.V.D NAVYA 121124

CIVIL ENGINEERING. K.SANJANA 121258

VIKI THAPA 121266

TOPICS COVERED

OBJECTIVE

INTRODUCTION

HISTORICAL PROSPECTIVE &

SIGNIFICANCE OF PROGRESSIVE COLLAPSE

REVIEW OF LITERATURE

o Typology

o Types of Failures

o Occurrence of progressive collapse

o Design Strategies

o Codes and standards

DESIGN &ANALYSIS USING SAP2000

RESULTS

FURTHER WORK TO BE CARRIED

REFERENCES

OBJECTIVE:

Progressive collapse analysis of reinforced concrete structures designed as per IS standards with special moment resisting frames, plastic hinges which account for robustness, byincluding nonlinear effects and dynamic analysis in numerical models and simulations, with the ultimate goal to develop better building evaluation and design guidelines for structural engineers to use to prevent progressive collapse in new and existing buildings.

INTRODUCTION:

Progressive Collapse

Progressive collapse of structures is characterized by a disproportion in size between a triggering event and the resulting collapse. In other words it occurs when the loss or failure of one member in a structure leads to loss or failure of other members, progressing through the structure and leading to partial or full collapse.

HISTORICAL PROSPECTIVE OF PROGRESSIVE COLLAPSE

This phenomenon was first realized after the progressive as well as disproportionate collapse of the Ronan Point apartment tower in England in 1968. The building had load bearing walls without any structural frame. A small explosion led to the failure of a load bearing wall which resulted in progressive collapse.

The Skyline Plaza (March, 1973), a large complex located in Virginia, was another case of such collapse. In midst of construction, one apartment building and the parking garage adjoining it collapsed. The root cause of the failure was premature removal of the form work triggering shear failure around a number of columns on the 23rd storey which led to the failure of 23rd storey followed by 22nd and so on causing progressive collapse. WTC is another important example of progressive collapse. Once the columns were destroyed by the plane crash, the alternative load paths were formed through the trusses. The columns were probably near, but not over, their ultimate load capacity. However, the fires proved fatal as the structural steel began to lose its strength at high temperature and after sometime, a complete structural collapse occurred.

SIGNIFICANCE

Significance of designing structures to resist progressive collapse has been recognised following the collapse of several structures, such as that at Ronan Point in 1968 and the collapse of World Trade Centre in 2001, where the consequences were deemed unacceptable relative to the initial damage.

LITERATURE REVIEW

Brief review of literature was carried in understanding typology of progressive collapse to its analysis including design strategies.

Types of Progressive Collapse

Classification of different types of Progressive Collapse based on mechanism of collapse was done by Uwe Starossek (i), they are

Pan Cake type Collapse Zipper type Collapse Domino type collapse Section type collapse Instability & mixed type collapse

Also classified the Collapse Promoting Features into the following types

Dynamic action, force concentration, brittle material behavior

Overstrength and ductile material behavior Structuredness

Elements of a progressive collapse and the probability of occurrence.

Mathematically, Probabilistic approach to the chain of events leading to a progressive collapse was formulated by Ellingwood [Ellingwood, 2002] because a progressive collapse consists of an initiating event, a local damage and structural collapse.

P(F) =∑ P [F∨DHi ]P[D∨Hi]P[Hi]

P(F) = probability of occurrenceP[F|DHi]= probability of collapse given initiating event and local damageP[D|Hi]= probability of local damage given the initiating eventP[Hi]= probability the initiating event or hazard

Design Approaches to progressive collapse

Three elements of progressive collapse were related to corresponding design approaches as

Initiating event - Event control. Local damage - Creating specific local

resistance. Structural collapse - Providing alternate load

paths.

1. Event control

It involves regulating or eliminating the probability of an event.

2. Specific Local Resistance

Creating specific local resistance is aimed at reducing damage to key structural elements when an initiating event or abnormal loading occurs.This approach addresses progressive collapse from the loading scenario point of view. Because this design approach explicitly provides strength to withstand a specific abnormal load, this approach is referred to as a direct design approach.

3. Providing alternate load paths

Related to this approach it is often noted that a structure should possess ‘general structural integrity’ or a certain level of ‘robustness’. By creating alternate load paths the robustness of a structure is enhanced.

Two ways of providing robustness is

Bridging Tying

PROGRESSIVE COLLAPSE ADRESSED IN STANDARDS &CODES

Prevention of progressive collapse became one of the unchallenged imperatives in structural engineering after such accidents. And, code-writing bodies and governmental user agencies attempted to develop design guidelines and criteria that would reduce or eliminate the susceptibility of buildings to this form of failure.

British Standard Code (BS 8110-1 1997 & BS 8110-2 1985) and Eurocode (EN 1992-1-1: 2004) have similar guidelines. They suggest designing the structure for accidental load and if not, then avoiding the situation where damage to small areas of a structure or failure of single element may lead to progressive collapse. The layout of the building is checked to identify any key elements, the failure of which would cause the collapse of more than a limited portion close to the element in question. This key element design must be taken into consideration. Elements other than key elements are provided with vertical ties in accordance with the code provisions.

Although there is no explicit mention of redundancy or alternate load paths in the American Code, it states to improve redundancy (ACI: 318-02). But U.S. General Services Administration (GSA Progressive Collapse Guidelines for New Federal Office Buildings and Major Modernization Projects 2003) and American Society of Civil Engineering (ASCE 7-02 Section 1.4) are two bodies which provide design guidelines for progressive collapse. While in INDIAN codes requirement for assessment was mentioned,

IS 15916 prescribes Design Requirements for Safety Against Progressive Collapse

IS 15988 in clause no 7.3 recommends to ensure that the failure of few elements shall not lead to loss of stability or initiate progressive collapse and hence recommends to be verified by a non-linear analysis such as pushover analysis, carried out upto the collapse load.

DESIGN AND ANALYSIS USING SAP2000

The General Service Administration guidelines for the design of government buildings [GSA 2000] provide explicit guidance on the use of linear analysis. While allowing nonlinear analysis, but does not give explicit guidelines.

It specifies that one column or section of wall is to be removed, and that gravity loads equal to 2(DL+0.25LL) are to be applied. Strength demands are calculated using static linear analysis, and the strength demand-capacity ratios are found.

DCR beam =MmaxMult

DCR column = PPy

+ Mpc1.18Mp

≤1

MODEL STUDIED

A simple model consisting of 2 bay-2 story is considered.

Cross-Section for Beam : 300mm X 500mm and Column : 400mm X 400mm are taken. Properties of materials

o Steel- fy = 250 Mpa

o Concrete M25 is considered

STATIC LINEAR ANALYSIS

Central Column in first story is removed for collapse analysis and

Load case of Dead Load with scale factor of 2 & Live Load with factor of 0.5 is defined and static linear analysis is carried.

Static Linear analysis implemented in Sap2000

STATIC NON LINEAR ANALYSIS

The same model is analysed for non linear static analysis as given in SAP manualfor both geometric and material non linearity.

Non-linear static analysis using SAP2000

LINEAR DYNAMIC ANALYSIS

This analysis procedure involves following steps:

Analysis is done as per GSA guidelines first for a column intact, then the column is removed and point load equal to the load carrying capacity is applied.

Dynamic load case is applied using time history and

analysis is carried

Dynamic Analysis using

SAP2000

RESULTS

It is inferred that accounting non linearity and dynamic

conditions has shown better results.

ONGOING WORK

The same procedure as done for the above model is followed for a RC structure with SMRF, and for different location of plastic hinges. DCR values in each case are found.

Results are analysed for conclusions and design strategies.

The work is further extended to seismic progressive collapse and evaluating different possibilities for various types of collapses.

REFERENCES

Typology of progressive collapse, Uwe Starossek

GSA, U.S. General Services Administration. 2003 (June). Progressive Collapse Analysis and Design Guidelines for New Federal Office Buildings and Major Modernization Projects. http://www.oca.gsa.gov.

Simplified Analysis of Reinforced Concrete Framed Structures for Progressive Collapse. AyushSinghania, VikasKhatuja, Vikram Thakur, Dr. C.B.K. Rao

Collapse Analysis Made Easy (More Or Less)Graham Powell Professor Emeritus, University of California at Berkeley

Various Procedures for Progressive Collapse Analysis of Steel Framed Buildings, Paresh V. Patel, Rushi Parikh.

IS15988 2013 SEISMIC EVALUATION AND STRENGTHENING OF EXISTING REINFORCED CONCRETE BUILDINGS — GUIDELINES

Parametric study of the progressive collapse of 2D framed structures Enrico Masoero, Falk K. Wittel, Bernardino M. Chiaia, Hans J. Herrmann