Progressive Collapse Resistance Research Articles

Analysis of Progressive Collapse Resistance in Precast Concrete Frame with a Novel Connection Method

The configuration of beam–column joints in precast concrete (PC) building structures varies widely, and different connection methods significantly affect the progressive collapse resistance of the structure. This study investigates the progressive collapse resistance of an innovative beam–column connection node frame. Finite element models of four-story, two-span space frame structures made of reinforced concrete (RC) and PC were developed using ANSYS 14.0/LS-DYNA R5.x software, employing nonlinear dynamic and static analysis to examine structural collapse behavior under bottom middle or corner column damage. Numerical results indicate that following the failure of the middle or corner column due to explosion loading, the vertical displacement and collapse rate of the PC structure with the novel connection method are less than those of the RC structure during collapse progression. Furthermore, upon removal of the middle or corner column, the residual load-carrying capacity of the PC structure with the innovative connection increased by 7% and 3.7%, respectively, compared to the RC structure. This suggests that PC structures with this type of connection demonstrate superior performance in resisting progressive collapse, offering valuable insights for future engineering applications.

Experimental and numerical investigation of punching and post-punching shear capacities of post-tensioned flat plate slab-column joints influenced by prestressing levels

Post-tensioned slab systems serve as an effective method to enhance the progressive collapse resistance of concrete flat plate structures by significantly improving the punching shear and post-punching capacities of their slab-column joints. While the existing research mainly focused on the punching shear behaviour of post-tensioned slab-column joints in small deformation stages, the post-punching behaviour in large deformations has been overlooked. This study aims to fill this research gap thorough experimental and numerical studies. Experimentally, four slab-column joints, including three post-tensioned specimens (with varied prestressing levels) and one specimen without tendons, were designed and tested. Detailed failure process and load-resisting mechanisms of the specimens at different deformation stages were discussed. The test results confirmed the efficiency of post-tensioning in improving the punching shear performance. Varying prestressing levels have influenced the development of punching shear capacity but did not affect the growth rate of load resistance in the initial post-punching stage. Numerically, validated finite element models were used to predict the post-punching capacities of the specimens. The numerical results indicated that post-tensioning helped increase post-punching capacities, but such an enhancement was independent of the prestressing levels. Additionally, the influence of the rupture strains of both tendons and reinforcement on the post-punching capacity was investigated through a parametric study.

Effect of steel reinforcement corrosion on progressive collapse resistant of beam-slab structure with interior column failure

To investigate the effect of steel reinforcement corrosion on the progressive collapse resistance of reinforced concrete (RC) structures, this study shows a methodology for establishing a finite element model (FEM) of a beam-slab structure by LS-DYNA software considering steel reinforcement corrosion. The reliability of this methodology was validated by experimental results. The analysis results indicate that considering the effect of the slab causes the beam-slab structure to enter the stages of tensile catenary action (TCA) and tensile membrane action (TMA) at smaller displacement. Moreover, as the corrosion time increases, the influence of the TCA on the structural resistance decreases. After prolonged corrosion, the top reinforcements of the beam at the failed column sides fail to fully utilize their tensile capacity when the structure fails. Furthermore, the corrosion of reinforcement significantly weakens the TCA and TMA to the structure, and neglecting the effect of the slab may lead to an overestimation of the weakening degree of the TCA caused by steel reinforcement corrosion. Additionally, the contribution of the slab's resistance in the beam-slab structure follows an "S"-shaped curve in relation to the displacement of the failed column, and the contribution of the slab to the structural resistance ranges between 40% and 60%.

Progressive Collapse Resistance Analysis of Plate-member Composite Reticulated Shell Structure

Progressive Collapse Resistance Analysis of Plate-member Composite Reticulated Shell Structure

Progressive collapse resistance of local prestressed concrete sub-structures: Numerical analysis and theoretical verification

The local prestressed concrete (LPC) structure is a structural form that combines the prestressed concrete (PC) span with the common reinforced concrete (RC) span, with significant asymmetry. Currently, there is insufficient research on the progressive collapse resistance of LPC structures. To investigate the progressive collapse mechanism of LPC structures, a parametric analysis was conducted by using the finite element software OpenSEES. Based on the failure mode of LPC structures, the proposed method predicted the limit state by considering displacement coordination, force equilibrium, and the influence of the plastic hinge regions. The research showed that LPC structures exhibited a distinct transition action stage (TAS) between the compressive arch action stage (CAAS) and catenary action stage (CAS), which distinguished them from the symmetrical structures. Increasing the strand area could significantly improve the catenary action (CA) of the LPC structure and extend the TAS. Lengthening the PC part also improved CA and allowed the structure to progress into TAS and CAS earlier. By increasing the length of the RC part, the compressive arch action (CAA) could be strengthened, while the duration of CAAS was extended. The theoretical prediction method proposed in this study can effectively predict the ultimate displacement and ultimate resistance of LPC structures.

Effect of three-dimensional space on progressive collapse resistance of reinforced concrete frames under various column removal scenarios

In this study, high fidelity finite element (FE) model was adopted to investigate the progressive collapse resistance of reinforced concrete (RC) frame structures under various column removal scenarios. The validity of the numerical model was verified by comparing with the existing experimental results. Afterwards, to facilitate the research on possible simplified boundary conditions served for further various column removal scenarios, the effect of multi-span continuous beams was firstly evaluated and the simplified methods were compared. Then, the effect of various column removal scenarios addressing the three-dimensional effect on the progressive collapse resistance of RC frame structures with and without slab was systematically evaluated. The analysis results showed that the continuous span beams increased the internal compressive force of the beam section at compressive arch action (CAA) stage, which effectively improved the CAA strength of the substructure. For simple modeling, the use of horizontal constraints at the end of the beam could replace the continuous span beams. The presence of transverse beams and slab provided additional load transfer paths for collapse resistance. The compressive membrane action (CMA) and tensile membrane action (TMA) of the slab significantly improved the progressive collapse resistance of the substructure in the small and large deformation stages, respectively. The location of the removed column significantly affected the contribution ratio of transverse beams and slab to the progressive collapse resistance of the substructure, which was quantitatively evaluated for practical design.

Experimental study on the progressive collapse resistance of emulative precast concrete beam-column subassemblies with various anchorage details

In this study, seven emulative precast concrete (PC) beam-column subassemblies with or without connecting bars and one concrete (RC) were fabricated and tested to investigate the effect of various types of anchorage detailing for reinforcing and connecting bars on the progressive collapse resistances. Two anchorage detailing formats for steel bars with bending and straight ends were used in the PC specimens for both the reinforcing and connecting bars. Test results show that, as found in the RC specimen, resisting mechanisms including pure flexure, compressive arch action (CAA) and tensile catenary action (TCA) were sequentially activated in all PC specimens. It is demonstrated that the connecting bars improved the progressive collapse resistance in both the CAA and TCA stages. The effect of the anchorage detailing was found to be negligible in CAA stage. However, in the TCA stage, the proper usage of the straight end for steel bars was helpful to improve the deformation capacity and thereafter enhanced the progressive collapse resistance. When the loading resistance, the deformation capacity as well as the construction flexibility are taken into account, the configuration consisting of both reinforcing and connecting bars with straight end as anchorage detailing is recommended for the design of precast beam-column connections in case a central column removal scenario is assumed.

Simplified test method for evaluating progressive collapse resistance of precast concrete frame structures

To evaluate the progressive collapse resistance of precast concrete (PC) structures, various test methods have been used in existing experimental studies. However, verification of whether the progressive collapse resistance can be evaluated equivalently by different test methods has been limitedly investigated. In this study, three simplified and three half-frame test specimens were tested under monotonic vertical loading to investigate the effects of the test method on their progressive collapse resistance. As the test parameters, types of test specimens (i.e., sub-frame, simplified, and half-frame specimens), and joint details (i.e., reinforced concrete (RC) continuous joint, PC with continuous joint, and PC with pinned joint) were directly compared. The test results showed that the progressive collapse resistance was primarily affected by the overall lateral stiffness of the exterior columns (Kh) rather than the test setup. When Kh increased in the simplified specimens, the axial force transferred by the beams increased, resulting in an increase in the peak strength (PCAA). Further, the effect of Kh on the peak strength was greater in PC specimens with pinned joints than in RC and PC specimens with continuous joints. To investigate the effect of Kh on the PCAA, a parametric study was conducted using the existing CAA strength model. The parametric study results also indicated that the relationship between the increase in Kh and PCAA was not significantly governed by the test setup for the same joint details. These results indicated that various simplified test methods can be used to evaluate the progressive collapse resistance of PC structures when an adequate range of Kh is provided. Based on the test and parametric study results, recommendations for progressive collapse tests were discussed.

Progressive collapse behaviour of earthquake-damaged interior precast concrete joints with headed bars and plastic hinge relocation

This study investigated progressive collapse behaviour of earthquake-damaged interior precast concrete (PC) joints with headed bars. The main objective was to quantify the impact of slight and moderate earthquake damage on their residual collapse resistance. The research began with a numerical investigation to understand the interaction between a 2D frame’s global response to seismic loading and its local response during a threat-independent progressive collapse event. Additionally, a separate set of numerical studies examined interior PC joints under cyclic loading to determine maximum drift ratio demands, yielding 2.5% for slightly and 3.5% for moderately damaged joints. Subsequently, an experimental programme under quasi-static loading conditions was conducted on five interior PC joints under cyclic loading, followed by progressive collapse resistance tests. Test results indicated that damaged joints exhibited flexural and catenary action during progressive collapse, but compressive arch action could not be mobilised due to residual cracks from the initial cyclic loading phase. Comparing damaged joints to fully intact ones from a companion study revealed deterioration in stiffness and deformation capacity during a subsequent progressive collapse, with degree of severity proportional to the extent of damage sustained in the cyclic loading phase. Relative to the intact joints without being subjected to cyclic loading, moderately damaged specimens exhibited a degradation of 63% in stiffness and 38% in deformation capacity, compared to slightly damaged specimens, which showed reductions of 38% in stiffness and 28% in deformation capacity. In contrast, strain hardening of steel bars in both slightly and moderately damaged specimens led to slightly greater collapse resistance than the intact joints. Additionally, failure mode shifted from ductile fracture to premature pull-through failure of headed bars in moderately damaged specimens. In this regard, in post-earthquake progressive collapse assessment, it is recommended to use maximum crack width thresholds of 0.2 to 1.0 mm for slight damage and 1.0 to 2.0 mm for moderate damage.

Progressive collapse resistance of precast concrete beam–column assemblies using dry connections under uniformly distributed loading condition

Improving the integrity of precast concrete (PC) frame structures using dry connections is essential for enhancing their robustness against progressive collapse. Therefore, three PC beam–column assemblies using different dry connections specially designed to ensure the connectivity were experimentally examined under progressive collapse scenarios. And a seven-point loading tree device was adopted to simulate the uniformly distributed loading conditions in practical engineering. The connection details were classified as follows: normal top-and-seat angle connection in TSA, strengthened top-and-seat angle connection in STSA, and strengthened top-and-seat angle with high ductility longitudinal reinforcements in the plastic regions in DSTSA. Under small deformations, STSA had the highest first peak load attributable to its strengthened joint connection. TSA obtained a lower load than that of STSA because of the low joint connection stiffness. Meanwhile, DSTSA achieved the lowest load among the three specimens because the smoother surface of the high-ductility reinforcements (compared with that of normal ones) weakened its bond to the concrete. However, under large deformations, the high ductility of the reinforcements ensured the specimen integrity; consequently, the largest final load was achieved in DSTSA. On the contrary, the high joint stiffness and normal reinforcements in STSA hindered the beam end rotation, and the steel angle failed early in TSA. As a result, the two connections failed to ensure the specimen integrity. To further shed light on the resistance mechanisms of beam–column assemblies under the uniformly distributed loading condition, an iteration-based model was developed to calculate the first peak load under the beam and compressive arch actions. The maximum prediction error achieved was 12%. Based on the model, the load contribution from the friction effect of the loading device was identified as 27%. And it was found that during the collapse, increasing reinforcement deformation region that might be induced by slippage between the concrete and reinforcements could lead to a continuous increase in the horizontal reaction force after the specimen reaching the first peak load.

Assessment of Different Methods for Enhancing Progressive Collapse Resistance of Irregular Reinforced Concrete Buildings Using Pushdown Analysis

AbstractEnsuring structures meet rigorous structural requirements is paramount in mitigating progressive collapse risk. In this comprehensive investigation, we scrutinize the impact of four distinct mitigation techniques on the propensity for progressive collapse in a six-story building featuring irregular structural attributes. The study adheres to the concrete building construction code ACI 318-14 and evaluates methods that include: (a) reinforcing the reinforced concrete (RC) slab with high-performance fiber-reinforced cementitious composites (HPFRCCs), (b) enhancing the RC slab with carbon fiber-reinforced polymers (CFRPs), (c) incorporating steel plate shear wall (SPSW) within specific columns, and (d) introducing an innovative approach named as the steel belt strip (SBS). In the context of 10 independent column loss scenarios conducted on the first floor, the nonlinear dynamic analysis reveals that HPFRCC effectively reduces vertical displacement under the removed column by up to 99.89% in certain scenarios. Meanwhile, the use of CFRP layers leads to reductions of up to 95% in vertical displacement, but with variations in effectiveness across scenarios. Notably, the SBS technique demonstrates remarkable potential by reducing vertical displacement by 97%, 89%, and 25.9% in different scenarios. This reduction, in conjunction with the mitigation of axial load on adjacent columns, makes the SBS a standout performer. Moreover, pushdown analysis indicates that, with the employment of these mitigation methods, the maximum loading factor can be increased up to 2.14 times in specific scenarios, significantly enhancing the structure’s resistance to progressive collapse. This pioneering research not only bolsters the resilience of irregular RC buildings but also holds profound implications for industry standards, risk assessment, and construction technology innovation.

Dynamic and uncertainty-based assessment of the progressive collapse probability of prestressed concrete frame structures with infill walls

Since progressive collapse usually has serious consequences, the problem of progressive collapse resistance has gradually become a topical issue in recent years. However, most of the existing studies have been conducted on common reinforced concrete (RC) structures. The methodologies used in the studies are also mostly static and deterministic. There is a lack of research that considers the dynamic effects and uncertainties of pre-stressed structures with infill walls. In this paper, the assessment of progressive collapse probability considering dynamic effect and uncertainties is performed for prestressed concrete frame with infill walls (IW-PC frame) structures. The finite element software OpenSEES is chosen as the analysis platform. By introducing uncertainties in material, geometry and load, five limit states and their quantitative indicators are identified. Based on the nonlinear incremental dynamic analysis (IDA) method, the vulnerability analysis of the IW-PC frame is performed under different working conditions. The vulnerability analysis indicates that the five levels of limit states can visually evaluate the degree of structural damage. Additionally, the resistance relationships of the four structural forms are as follows: IW-PC frame > reinforced concrete frame with infill walls (IW-RC frame) > prestressed concrete frame (PC frame) > RC frame. The load carrying capacity of the frames is significantly increased by the coupling effect of the infill walls and the prestressed strands. Moreover, the prestressed strands can reduce the probability of light and moderate damage, while infill walls have an excellent preventive effect on severe damage. The reliability of the four structures is evaluated using the Zhao-Ono moment method. The results indicate that IW-PC is the safest, followed by IW-RC, PC, and RC.

Progressive collapse analysis on modular steel construction based on a simplified joint model

Modular steel construction (MSC), as a kind of highly prefabricated assembly building, has the advantages of high industrialization, perfect energy saving and great being environmentally friendly. Due to the special characteristics of its detail construction, there is an urgent need to study its progressive collapse resistance performance. Based on the experimental and refined simulating results, a simplified model of inter-module connection was proposed and shown to be accurate enough for capturing the collapse properties of the MSC by comparing with a sub-structure push-down test. Then the collapse responses of a typical four-story, nine-span MSC under different local failure conditions were intensively studied using the proposed model. The MSC survived in the local failure scenarios of the side-columns, the corner-columns or even the mid-modular unit. However, in the scenario of side-modular unit failure, the inter-module connections of all four stories were damaged due to excessive overturning moments, leading to the collapse of the span where the unit fails. Nevertheless, the rest part of MSC still did not collapse. Therefore, it can be concluded that the modular steel construction with inter-module connections by bolts and shear keys has good performance on progressive collapse resistance. Moreover, further research into this type of inter-module connection would be worthwhile.

Evaluation on the failure modes and progressive collapse resistance of self-centering infilled precast concrete frame

In this study, the refined finite element (FE) models for the collapse resistance of self-centering precast concrete (PC) frames with and without infill walls were established. Based on the validated FE models, the effects of different design parameters on the failure modes at the beam ends as well as the collapse resistance of the structures were evaluated. Correspondingly, the reasonable optimization measures were suggested to reduce the concrete damage at the beam ends. The results indicated that the insufficient stirrup spacing may cause the concrete failed prematurely along the edge of the steel jackets due to stress concentration. Decreasing the thickness of steel angles could reduce the failure area of concrete at the beam ends, but also caused a significant reduction in the initial stiffness and vertical resistance of the structures. The thickness of steel jackets mainly influenced the size of failure area at the beam ends. The position of horizontal bolts and longitudinal bolts had effects on the failure modes of concrete at the beam ends as well as the collapse resistance of the structures, while the latter was particularly evident. Compared to the cast-in-place reinforced concrete (RC) frames with the same size and reinforcement ratio, the damage extent at crucial locations of the optimized self-centering PC frame structures was lower, while exhibiting similar collapse resistance. A calculation model considering the resistance contribution of structural and non-structural infill wall members was proposed to predict the vertical resistance of self-centering PC frame structures in the compressive arch action (CAA) stage. The accuracy of the calculation model was verified by comparing 23 FE models with different design parameters.

Study on the mechanism and countermeasures of progressive collapse in deep excavation retained by multilayer struts

There is still a lack of research on the resilient design of excavations retained by multilayer struts against progressive collapse. This paper utilizes a discrete element method (DEM) model to investigate the mechanism of the force variation in struts and diaphragm walls during excavation and progressive collapse based on the Nicoll Highway accident in Singapore. This study identifies dangerous time points, which occur after the excavation has reached a certain depth, leaving a layer of soil without a corresponding strut. At these points, the bottommost one or two installed struts and diaphragm wall are critical components that can trigger progressive collapse if they fail. To prevent this, two concepts are proposed and are validated by DEM simulation. The sparse upper and dense lower (SUDL) strut arrangement concept ensures progressive collapse resistance of the retaining structure at the bottom of the excavation. The concept of dynamic redundant struts (DRSs) utilizes redundant struts to provide temporary protection in the vulnerable sections of the retaining system during excavation. Alternating the installation and removal of DRSs creates dynamic redundancy, ensuring progressive collapse resistance throughout the construction process in a relatively economical way. Additionally, the DRSs can effectively reduce the lateral deflection of the retaining wall.

Evaluation of progressive collapse resistance performance of steel OMF with WCPF connections

A welded cover plated flange (WCPF) connection, which is a pre-qualified connection detail improving a weak weld access hole and the ductility of a welded unreinforced flange-bolted web (WUF-B) connection, has a simple and efficient advantage in construction. In this study, a new modelling approach of the WCPF connection by employing 1-D element was proposed for the evaluation of progressive collapse resistance capacity performance. The model was developed by substituting the average width of trapezoidal shapes of cover plates welded to the top and bottom flanges and by assessing the equivalent flange thickness based on the moment of inertia. The proposed model was verified through comparisons with experimental and 3-D numerical results, showing discrepancy within 5.7%. To evaluate the performance of the WCPF connection, a prototype structure was adopted from the previous study for the appraisal of the WUF-B and reduced beam section (RBS) connections. The alternative load path method was performed using an energy-based approximate analysis considering the dynamic effect of sudden column loss. The performance of the structure was evaluated in terms of structural robustness and sensitivity. Furthermore, the results were compared to those of the structures with the WUF-B and RBS connections analyzed in the previous study. The structure with the WCPF connections showed 33% more improved structural robustness and 11% less sensitivity to progressive collapse when one column was removed. In a two-column removal scenario, only the structure with WCPF connections indicated to have proper progressive collapse resistance capacity. The WCPF connection was deemed more reliable than WUF-B and RBS ones.

Progressive Collapse Resistance Assessment of a Multi-Column Frame Tube Structure with an Assembled Truss Beam Composite Floor under Different Column Removal Conditions

To estimate the progressive collapse resistance capacity of a multi-column frame tube structure with an assembled truss beam composite floor (ATBCF), pushdown analysis and nonlinear dynamic analysis are conducted for such a structure using the alternate load path (ALP) method. The bearing capacities of the remaining structures under three different work conditions, which are the side middle column removal, the edge middle column removal, and the corner column removal, are individually studied, and the collapse mechanism of the remaining structures is analyzed based on the aspects of the internal force redistribution and the failure mode of the second defense line. Simultaneously, the influence of the column failure time on the dynamic response of the remaining structure and the dynamic amplification coefficient is discussed. The results indicate that the residual bearing capacity of the remaining structure following the bottom corner column removal is higher than that of the one following the side or edge middle column removal, while the latter has a stronger plastic deformation capacity. When the ALP method is adopted to operate the progressive collapse analysis, it is reasonable to take the column failure time as 0.1 times the period of the first-order vertical vibration mode of the remaining structure, and it is suitable to set the dynamic amplification coefficient as 2.0, which is the ratio of the maximum dynamic displacement to the static displacement of the remaining structure under the transient loading condition.

Whole-process analytical model on progressive collapse response of reinforced concrete structures under middle column loss

Since progressive collapse is essentially a dynamic process, the whole-process resistance evolution path is critical for a structure against progressive collapse. Previous analytical studies focus primarily on one particular phase of a single load transfer mechanism, such as compressive arch action (CAA) or catenary action (CA) capacity. This study develops a unified analytical model to evaluate the whole resistance-displacement curve of reinforced concrete (RC) structures. In the analytical model, compatibility, equilibrium condition, constitutive laws of concrete and reinforcing bars, and fracture of reinforcing bars are considered. To avoid complex iterations, curvature equations and combination schemes of cross-sectional forces are also established. The analytical model is verified against experimental resistances and axial forces of RC beam-column substructures measured in 24 tests, and it is subsequently utilized to illustrate the evolution of cross-sectional forces throughout the loading process. Furthermore, a sensitivity analysis based on the K-L entropy index is conducted to quantify the effects of different parameters on the progressive collapse resistance. The results show that the yield strength and diameter of reinforcing bars are vital to the whole resistance curves. The axial stiffness and beam depth primarily affect CAA capacity, while having a less significant impact on the CA capacity. Fracture displacement of reinforcing bars is the most influential parameter for CA capacity, suggesting the importance of considering the fracture of reinforcing bars in the analytical model.

Finite element analysis of progressive collapse resistance of precast concrete frame beam-column substructures with UHPC connections

Compared with reinforced concrete structure, precast concrete structure is prone to progressive collapse due to its poor continuity. The use of ultra-high performance concrete (UHPC) provides a feasible solution. To this end, investigate the influence of UHPC on the progressive collapse resistance of precast beam-column substructures, the finite element model of precast beam-column substructures with UHPC connections was established. The model was validated using available experimental data. Specifically, the cohesive-Coulomb friction model was used to simulate the interface behavior between precast concrete and cast-in-place concrete, and the metal ductile damage model was used to simulate rebar failure. The finite element simulation results show good agreement with experimental results, with an average error of less than 5 %. Additionally, five sets of full-scale analysis models were designed to analyze the effect of cast-in-place UHPC on the progressive collapse resistance of precast beam-column substructures. The results indicated that UHPC enhances the compressive arch action (CAA) capacity and catenary action (CA) capacity of precast beam-column substructures. Parametric analysis was conducted based on these models. The results indicated that the increase of UHPC strength grade can improve the CAA capacity of the structure, but reduce the CA capacity. Interface roughness has a certain effect on CAA capacity, but has no obvious effect on CA capacity. Finally, the accuracy of existing analytical models in predicting the CAA and CA capacity of UHPC-connected precast beam-column substructures is evaluated. The research results can provide reference for the design and application of precast concrete structures connected by UHPC.

Multi‐indicator evaluation method of important members of truss string structures

SummaryDuring the past decade, the progressive collapse of structures has received growing attention, and the study of member importance is a key step for investigating the progressive collapse resistance. However, traditional methods for evaluating the member importance usually employ a single indicator, and when multiple indicators are involved, different indicators may generate different member rankings. Moreover, the truss string structure is a multiple super‐stationary structure with many members, and the current studies mainly focus on cable failure, which does not mean that other members are not important. In this study, the initial selection of important members is first performed based on concept evaluation, and then, the alternate path method is used to analyze the progressive collapse resistance of truss string structures; the slope degradation coefficient γ of incremental dynamic analysis curve, load capacity degradation coefficient β, and nested load capacity degradation coefficient β′ are introduced; and the sensitivity coefficient SIj and fragility coefficient VIi are defined with axial force as the structural response. Based on the above five indicators, two cases are conducted to evaluate the member importance. The analysis results show that the cable and the bottom chord member at the support are evaluated as the first‐level important members. Through the analysis of different indicators, it is found that the regularity of the coefficient of each member is inconsistent for different indicators. The results could be one‐sided if the important members were evaluated by a single indicator only. In addition, the second‐level important members of truss string structures are evaluated by multi‐indicator analysis. Finally, the nominal progressive collapse resistance of truss string structures is given based on the importance coefficient of the first‐ and second‐level important members.