Demand Capacity Ratio Research Articles

Progressive Collapse of Flat Slab Buildings

Progressive collapse occurs when a local failure triggers successive failures leading to total collapse of the structure. In this project, progressive collapse analysis has been done using a finite element linear static and a non linear static analysis on a 6 storey flat slab building. Though there are dynamic methods also for the analysis but static method has been used owing to its practicality and simplicity in engineering world. Dynamic method is more complicated and involves a number of iteration before it can give any close to accurate result, hence is not in much demand nowadays. The results for the linear static analysis have been compiled in the form of demand capacity ratio at critical section and results for that of the non-linear static analysis have been compiled in the form of support rotation at joints. In both the case the building is not susceptible to progressive collapse both when the central column is removed and the corner column is removed.

Progressive Collapse Analysis of T shape RCC Building

Structure collapse, on the other hand, is a very complicated phenomenon involving considerable nonlinearity and a variety of mechanical interactions. It should be thoroughly examined through experiments and numerical simulations to prevent the occurrence from occurring. When initial local failure of a small portion of the structure takes place it leads to the spread of that local damage to neighbor elements in the chain reaction manner. Finally, collapse takes place. This is known as Progressive collapse. This progressive collapse takes place when vertical load carrying members such as columns failed due to manmade or natural accidental loads. Therefore in this study progressive collapse analysis of a building is carried by removing columns. In the analysis different column removal cases are considered. As per GSA guidelines, Demand Capacity ratio(DCR) of beams are calculated. From this DCR value Evaluate the stability of the structure against progressive collapse. In the present study “T”shape building is considered which consists of 11 storey with bay sizes as 4 meter in the X and Y direction, height of every storey is 3 meters and height from the plinth to the floor is assumed 3.5 meters. The measurements of the beams are fixed throughout the storey, but column dimensions decrease as the floor rises, therefore the structure is considered to have geometrical irregularity. The loading is calculated in accordance with G.S.A guidelines. The design was created using the ETABS software and the I.S 456-2000 code. Different parameters such as Demand-capacity ratio, Dynamic factor, Interaction ratio, Axial Force, Bending moment are discussed.

Evaluation of progressive collapse behavior in reinforced concrete buildings

Progressive collapse is a catastrophic chain reaction of failure of a structure that is caused due to loss of vertical load bearing element of the structure, resulting damage of a part of the structure or entire structure. In our research work 10 storey regular Reinforced Concrete framed structure is considered and is seismically designed with IS 1893:2016 in SAP2000 version 20 modeling. The different column removal scenarios both in plan and elevation suggested by guidelines were examined by alternate load path method using nonlinear staged construction available in the software and then identify the potential of the structure to withstand progressive collapse. Numerical results were compared by analyzing columns and beams separately by calculating demand capacity ratios and the requirement of percentage of steel for failed structural elements are predicted both in flexure and shear stresses. Our objective is to provide clear conceptual step-by-step descriptions of various procedures for progressive collapse analysis 3D (three-dimensional) Finite Element Methods (FEM) and non-linear static push-down analysis in SAP2000 software was used to assess the progressive collapse potential of a typical gravity-load designed mid-rise reinforced concrete building with open ground floor. The beam is actually designed to resist the shear force up to 39.84 kN. So in order to resist the shear failure we need to provide enough vertical reinforcement. The failed structural elements were re-designed to resist progressive collapse in order to satisfy the acceptance criteria recommended by the guidelines. It’s showed that the incorporation of perimeter beams in buildings improved the progressive collapse resistance as it reduces joint displacement and chord rotation at column removal locations by providing sufficient stiffness and load paths for increased gravity loads. The study results can be used to develop and calibrate the nonlinear numerical model for analyzing high-rise building progressive collapse behavior and can help provide information that may improve new and existing reinforced concrete core-wall building robustness against progressive collapse.

FE modelling progressive collapse assessment of steel moment frames-parametric study

ABSTRACT Progressive collapse is the failure of primary structural components produced by natural or abnormal events that may result in a total or partial collapse of the structure. In this paper, several structure models, under different column removal scenarios, were modeled and analyzed using the FE program SAP2000 to evaluate the effect of span length, the strength of structural members, and cross-section on the steel building’s resistance against progressive collapse. The Alternative Load Path method was carried out using the linear static and nonlinear dynamic analysis following the GSA 2003 guidelines for this investigation. The material and the geometric nonlinearities must be considered in the nonlinear dynamic analysis. The contribution of span length, steel grade, and cross-section to the response of the structural system was studied through the Demand Capacity Ratio for the linear static analysis. The variation of several parameters, such as bending moments, plastic hinges status and their rotations, displacements, and ductility, was discussed based on the response of the nonlinear dynamic analysis. The main objective of this study is to demonstrate the impact of the latter parameters on the structural enhancement and the reduction of the damage level triggered by the failure of a primary structural component.

Seismic vulnerability analysis of simply supported continuous bridge during construction

PurposeIn order to explore the damage probability of bridge engineering in the event of earthquake in the construction stages, the analysis method of seismic vulnerability in the construction stages is proposed in this paper.Design/methodology/approachBased on the joint simulation function of construction stage conditions and seismic response conditions of MIDAS/Civil finite element analysis software, combined with the method of IDA analysis and compared the relationship between demand and capacity.FindingsThe research shows that: (1) the average seismic loss in different construction stages varies greatly; (2) the seismic vulnerability varies greatly in different construction stages. The vulnerability of the bridge in stage 6 is determined by the longitudinal direction of bridge. Therefore, during the construction of the whole bridge, we should focus on strengthening the disaster and loss prevention strategy of earthquake insurance in the longitudinal direction of bridge. (3) The application of the secondary dead load mainly affects the fragilityin the longitudinal direction of bridge, but has little effect on the fragility in the transversal direction of bridge.Originality/valueThis paper is to explore the seismic vulnerability of a typical simply supported continuous bridge during the construction stages, and to trace the entire construction stage of a typical simply supported continuous bridge. According to the characteristics of the system transformation in the actual construction steps, demand-capacity ratios were established based on incremental dynamic analysis (IDA) and performance indicators of moment curvature and stability, and the seismic vulnerability research is carried out for the construction stages prone to earthquake damage. Furthermore, it provides a basis for seismic risk assessment of such bridges in different construction stages.

Effect of vertical-to-horizontal acceleration ratio of earthquake components on the utilization of buckling-restrained braces in steel frames

This paper presents an approach to design the buckling-restrained braces (BRB) system based on the resisting work of the steel braced structures to mitigate the structural seismic collapse. This approach covers the influence of different structural brace variables, the vertical-to-horizontal acceleration ratio (V/H ratio), and the percentage of brace utilization on structural resistance to seismic collapse considering column loss. The determination of this column loss relies on the probabilistic calculation of the critical demand-capacity ratio of the column element that poses the highest threat to fail under large lateral displacements. The investigation uses thirty-six archetypes of steel braced structures with regard to the V/H ratios and various structural parameters related to the bracing systems. The results of the proposed BRB design expand the role of the bracing systems from the protection of the structure against the lateral loading to the prevention of the vertical structural collapse.

Comparison of thickness shear wall against drift floor using pushover method

Lateral load or earthquake disaster can damage the structure of a highrise building. Therefore, calculations are needed to avoid massive damage to the structure when an earthquake occurs and give a load to the structure. One of the efforts that is done to resist the earthquake is using shear wall. On this research, there will be a comparison of shear wall thickness that will be used for the building model. Where there is existing model with the shear wall thickness 400 mm, modified model with the shear wall thickness 350 mm and 300 mm, and model without shear wall. Earthquake standards is using SNI 1726-2019, load standards are using SNI 1727-2013, concrete design is using SNI 2847-2019, and for the structure analysis is using ETABS Program. First step is calculating the Demand Capacity Ratio (DCR) of the structure element to determine if the structure needed to be analyse using non-linear static (pushover) or not. And then there will be drift ratio calculation to determine the building performance level using Federal Emergency Management Agency (FEMA) 356 provisions.

Effect of hanger system on resistance against progressive collapse of RC buildings under column removal in alternate storeys

Progressive failure refers to the continuous disintegration of a structure until partial or complete collapse, resulting in severe economic losses and mass casualties. The present study proposes a feasible solution against progressive collapse by the introduction of a hanger system and highlighting its effect on R.C. building under the progressive collapse scenario. The hanger system mainly comprises of a structural wall enacted at the terrace level in place of the parapet wall, which acts as a highly stiff member connecting the columns in various bays and allowing load transfer between these bays, thus creating an alternate path for loads. This study follows the removal of various critical columns on the alternate storeys, in contrast to previously conducted researches which were focused on only removing selected columns on the ground storey. CSI's ETABS 19 software has been used to simulate the progressive collapse of a reinforced concrete building, assessing the behaviour of a 10 storey reinforced concrete building under progressive collapse, with and without designing structural wall at the parapet, using static linear analysis of progressive collapse compliant with the general service administration guidelines (2016). In all the cases of removal of critical columns, the results are compiled in respect of DCR values (Demand Capacity Ratio) at critical locations and joint displacement at the top of removed columns. The hanger system used in this study provides an innovative and feasible solution to prevent progressive collapse by providing alternate load paths and increasing the robustness of the building.

Progressive collapse of irregular RC building

Progressive collapse occurs when one of a structure's essential elements fails, causing subsequent structural elements to fail as well, resulting in the entire structure or a portion of it collapse. The failure of a structure's vertical element is the most common cause of the structure's progressive collapse. Blast loads, accidents, or intentional destruction can all cause a column to fail, resulting structural collapse. The influence of column failure on an irregular reinforced concrete (RC) building of G + 5 storey is explored in this study. To better understand the structure's seismic behaviour, a non-linear static analysis (NSA) is conducted using General Services Administration (GSA) loading and establishing the crucial points in the structure that are prone to collapse. The demand capacity ratios defined using linear static analysis (LSA) are compared to the hinge formation derived from NSA at important locations. The behaviour of the progressive collapse analysis is investigated when a sudden column loss occurs due to the impact of the blast load. The collapse resistance of a structure is determined when it is subjected to blast loads. The DCR values were calculated and compared to the acceptance criteria in the GSA guidelines, and it was revealed that the DCR values obtained surpassed the acceptance criteria. The design has been discovered to be prone to progressive collapse, and regular design considerations must be followed to avoid this failure.

Linear static progressive collapse analysis of RC structures

When there is a sudden loss of load carrying element in a structure, the structure will choose alternate load paths until equilibrium is reached. In this process, elements overloaded in the alternate load paths fails, leading to a large damage disproportionate to the initial event which is referred to as Progressive Collapse (PC). Fire, gas explosions, terrorist attacks, car crashes, and improper design and construction are all common causes of progressive collapse. As a result, it is important to research and examine the effects of this phenomena on structures, as well as to reconstruct the structure to be resistant to it. Government buildings, hotels, offices and residential buildings require different spacings and may require large spans. Though lot of research work has done on PC resistance of Reinforced Concrete (RC) structures to explore that research, in this study, RC buildings with 4 m, 6 m and 8 m clear span between columns have taken and linear static analysis (LSA) has done for different column removal conditions. PC resistance is measured in terms of vertical joint displacement (VJD), chord rotation (CR) and demand capacity ratio (DCR). The VJD and CR results are discussed and compared with each other. The calculated CR values and DCR values are compared with the limiting value as mentioned in GSA and DoD. The tendency to PC is more for 8 m span model is more than the other models with 6 m and 4 m.

Effects of the vertical component of ground motion on the seismic performance of Bhakra Gravity Dam

In this paper, the earthquake component effects on the seismic performance of Bhakra Gravity Dam in India are investigated. For the purpose, Bhakra Dam is modeled two-dimensionally considering dam-reservoir-foundation interaction. In the finite element modeling, dam and foundation are represented by PLANE182 elements in ANSYS with different material properties, and fluid is considered with FLUID29 elements. This type of element provides translation and pressure degrees of freedom. Linear time history analyses on the dam are performed by considering components of the 1991 Uttarkashi and 1999 Chamoli (NW Himalaya) Earthquakes in India. During the analyses firstly the horizontal component of earthquakes are applied to system and results are obtained, and then both of horizontal and vertical components are applied to the systems together. In the analyses, element matrices are computed using the Gauss numerical integration technique. The Newmark method is used in the solution of the equation of motions. Also, Rayleigh damping is considered. The seismic performance of Bhakra Dam is examined and presented by dynamic characteristics, displacements, principal stresses, and demand-capacity ratios. The results showed that the vertical components of the earthquake significantly affect the response of the dam. The results show that the vertical component with the horizontal component cause biggest tensile stresses compared to only the horizontal component for both earthquakes. However, displacement response is changed depending on the ground motion. As a conclusion of this study it can be said that the vertical component changes the structural response of the dam on both of the good and bad behaviors.

Seismic performance analysis of retrofitting building structure with type X bracing

The result of the earthquake causes a lateral force that occurs on the building structure. Loads caused by earthquake loads need to be calculated and designed based on standards, so that when an earthquake occurs, the structure of the building is still able to resist the resulting lateral forces. The calculated building structure has a height of 12 floors with structural elements consisting of columns, beams, and shear walls. This building structure is loaded with earthquake loads which refer to SNI 1726-2019 Procedures for Earthquake Resistance Planning for Building and Non-Building Structures. Based on the calculation of the existing building structure due to the earthquake load of SNI 1726-2019, it was found that the story drift and Demand–Capacity Ratio (DCR) in column and beam did not meet the planning standards. The building structure was remodeled using type X bracing retrofitting to determine the value of story drift and DCR. Building structure modeling with type X bracing consists of three model shapes varying the location of placement and the number of type X bracing per floor. The results show that the addition of type X bracing can reduce the story drift up to 32.77% for the x direction and 33.75% for the y direction. In the cross-section of the beam element, the reduction in internal forces can reduce the Demand–Capacity Ratio (DCR) value in the beam. The cross-section of column element, the internal force has decreased but for the column which is attached to the type X bracing system showed an increase in internal force which causes an increase in the DCR value.

Progressive Collapse Behaviour Assessment of Steel Frame Structures – A Review

In building construction, steel structures are favoured as they have some advantageous properties, such as high strength, light weight and high construction performance. However, there are few disadvantages since steel structures are prone to incremental collapse caused by accidental scenarios in which structural components are weakened or eliminated, leading to structural failure. Many research studies have been carried out on steel frames are generally for single column removal scenario. Since more than single structural members may be affected during accidents, numerous column removal scenarios need to be investigated to assess the progressive collapse of steel frame. This reviews study on how the steel frame structures can be simulated numerically using various finite element software to determine progressive collapse resistance for steel frames for different Progressive Collapse scenarios. It is found that Demand Capacity Ratio (DCR), Dynamic Amplification Factor (DAF) and Robustness Index for the critical points are some of the parameters to check the stability of the steel structures due to Progressive collapse scenario.

Progressive Collapse of a Single Layer Schwedler Dome

Large span domes have always drawn architects’ and engineers’ interest as they provide as easy method of roofing large areas with architectural beauty. Single layer Schwedler Dome composed of Circular Hot Hollow Frame (CHHF) is investigated to understand the effects of individual member removal to the behaviour and stability of single layer dome. The major issues of the structural system are related to its instability phenomena whereby it is vulnerable to snap through buckling. The failure of space structure such as Sultan Zainal Abidin Stadium and Bucharest Dome clearly show an understanding of such failure and the behaviour of the space structure is important to develop a safer structure especially in the future. This study deals with a single layer dome having a diameter of 52 m and the span to depth ratio of ½. The loads subjected on the nodes of the structure consists of dead, live and wind loads and assumed to be 1kN each. Due to the symmetric geometry of the dome, the removals were done on the quarter section of the dome only assumed that the loads distribution patterns are similar for each section. This study required 210 members’ removals and the result obtained has been analysed thoroughly. In order to achieve the objectives of the research, computer programming such as FORMIAN, AutoCAD and SAP2000 V18 have been used to generate the geometry of the dome and afterwards analysed the stability of the structure. The numerical technique is based on redistribution of internal loadings due to member’s failure. Critical members are determined by analyzing the Demand Capacity Ratio (DCR) value of each member and identifying the number of overstressed neighboring members. When the internal load of a neighboring member exceeds its loading capacity, the member becomes overstressed and fails which may lead to major collapse of the entire structure. The value of the DCR and the numbers of overstressed members existed in the structure after the removals show the criticality of the section. As a conclusion, this critical area must be considered during analysis, design and construction stage of the dome.

Behaviour of moment resisting reinforced concrete frames subjected to column removal scenario

Researchers awarded a considerable attention to progressive collapse analysis in recent years to avoid the partial or entire failure of structures. General Service Administration guidelines (GSA) established the base to deal with such catastrophic failure. For multi-story building, these guidelines proposed column removal scenario in which one or more columns in different locations should be removed from a structure. Then, the response of entire structure with the column omitted should sustain the loading applied ensuring no global failure occurred. In this paper, three-dimensional reinforced concrete (RC) frame is constructed and analyzed using the commercial program SAP2000. Non-linear static analysis is employed to obtain Demand Capacity Ratios (DCR) for beams and the displacement of joint connecting beams to column in the selected frame. The response of moment resisting RC frame under column removal scenario is presented and discussed in terms of strength and displacements in critical locations in RC frame to evaluate the strength of such frame against progressive collapse.

A Methodology of Evaluating Urban Parking System: Case Study of Delhi

A parking study is carried out in the NCT of Delhi to measure the parking system performance for different land-uses. Various parking statistics such as parking demand, demand-capacity (D/C) ratio, parking load, parking efficiency, and utilization are considered to demonstrate the parking conditions and problems at the selected parking locations. Further, four key-indicators viz., D/C ratio, search + park time, walk time and parking fees are chosen to develop parking performance index (PPI) which evaluate the parking facility from users’ perspective. PPI is a single value index, which is estimated by combining the evaluation criteria of the four indicators using a radial coordinate system. PPI is classified into four categories: Excellent, Good, Fair and Poor using clustering analysis in order to define the thresholds for each category. The paper demonstrates the case study application, which describes the applicability of the developed PPI at three locations in Delhi. Lastly, a few parking strategies and guidelines are discussed based on the analysis, on-field survey observations, and past literature. The proposed method can be adopted globally with the required modifications. The study is helpful for the transport planners and policy-makers to quantify the quality of the existing parking system, and the improvement plans can be made accordingly.

Improved progressive collapse resistance of irregular reinforced concrete flat slab buildings under different corner column failures

As the flat slab building with irregular geometric configurations is commonly designed to advance urban development and for architectural demands, its behaviour to resist progressive collapse must be examined. The building's progressive collapse occurs when one or more vertical structural load-bearing elements such as columns are removed due to an extreme load caused either by natural or manmade hazards. The present analytical research examines the failure criteria and improvement in the progressive collapse resistance of five and ten-storey irregular R.C flat slab building by incorporating perimeter beams along with strengthened perimeter columns in the building. The progressive collapse study is conducted by removing different corner columns on the ground floor as per the GSA guidelines (2003) and assessing the spread of damage. Static analysis is performed using the structural analysis program ETABS 2016. For each case, the results have been taken in terms of demand capacity ratio (DCR) at critical sections and, chord rotation and joint displacement at locations of removal of columns. The results showed that the presence of strengthened columns provides sufficient stiffness and the perimeter beam provides load paths for the building's gravity loads, thus making it resistive to progressive collapse under column failure.

Research on seismic fragility analysis of regular bridges based on response spectrum analysis method

In this paper, the incremental dynamic analysis (IDA) of a real bridge is carried out by using the nonlinear time-history analysis method and the response spectrum analysis method respectively, and the results of structural response under different earthquake intensity are obtained. Ductility coefficient is used for damage index, and the damage probability of the structure in different damage state is obtained by using logarithmic demand-capacity ratio, and then the seismic fragility curves of the structure are established. To improve the precision of fragility curve of major damage state and failure state by modifying the fitting function is also studied. The results show that the simple linear elastic method is reliable for calculating the seismic response of regular bridges. The seismic response calculated by the response spectrum analysis method could be used as the demand for establishing the fragility curves of regular bridge.

Evaluation of seismic torsional response of ductile RC buildings with soft first story

This study investigates the inelastic torsional response of plan asymmetric ductile RC buildings with a soft first story. The buildings of Rectangular, L, T, and U plan shapes are considered for the study. Force-based fiber beam-column elements are modeled for the inelastic response prediction of the buildings. Masonry infill walls are uniformly distributed in the plan and considered for the evaluation of torsional response. The pushover methods, Extended N2 and Extended Capacity Spectrum Method – FEMA 440 are adopted to estimate the inelastic torsional response. Bi-directional nonlinear time history analysis is carried out on the buildings considering near-field and far-field ground motions. Story drift ratio and curvature demand-capacity (D/C) ratio of columns are reported at the stiff, flexible side of buildings. The torsional response of infill wall buildings is compared with that of bare frame buildings. It was observed that the torsionally irregular ductile buildings with soft first story exhibit higher seismic demand on the flexible side corner columns. Infill wall interaction amplifies the torsional response at the bottom story, causing an increase in displacements higher at the flexible side and moderate near the stiff side. This study concludes that the flexible side corner column in plan asymmetric building with a soft first story can be conservatively designed for 1.5 times the design forces obtained from the analysis. This conservative design ensures stable energy dissipation in the corner column under load reversals, without significant strength reduction under higher excitation levels. The designer shall properly distribute lateral load resisting elements in a plan to prevent premature failure of the columns located internally and close to the initial center of rigidity. The designer can avoid the collapse of columns located internally in the buildings with stiff peripheral frames by designing for forces 1.5 times higher than obtained.

Dynamic analysis of high-strength concrete frame buildings for progressive collapse

The issue of progressive collapse of two real-scale frame buildings examples (three and six stories) constructed from High-Strength Concrete (HSC with fc` =75 MPa) and Normal-Strength Concrete (NSC with fc` =32 MPa) under central column removal have been studied using numerical analysis. Initially, a finite element linear static analysis was carried out. Next, linear dynamic and non-linear dynamic analyses were conducted to account for the extreme dynamic effects that arise during central column removal. The values of Demand-Capacity Ratios are considered in each analysis. The results showed that, the analysis of progressive collapse under central column removal of three and six stories frame buildings constructed from HSC is approximately similar to that of the same structures constructed with NSC. The three stories building constructed from NSC and HSC would not be susceptible to collapse for linear statically central column removal, while the situation is reversed for both NSC and HSC six stories buildings. NSC and HSC three and six stories buildings would be susceptible to progressive collapse for linear and nonlinear dynamic central column removal. The ratio between the maximum nonlinear dynamic displacement and the maximum linear dynamic displacement for NSC and HSC three stories buildings at the column removal are 1.17 and 1.18, respectively, whereas these ratios become 1.89 and 1.86 for NSC and HSC six stories building, respectively. The internal forces at the most critical sections for NSC and HSC three story building in the case of linear dynamic analysis are larger than that of linear static analysis by about 58% and 39%, respectively, while for six story building these ratios become 82% and 80%, respectively. For the case of nonlinear dynamic analysis, these ratios for NSC and HSC three story building are larger than that of linear dynamic analysis by about 9% and 7%, respectively, while for six story building these ratios become 11 % and 8%, respectively due to activation of plastic hinges.