Search

At present, the main methods of bridge condition assessment are reliability analysis and analytic hierarchy process method. Robustness, as a measure of the structural ability to maintain the performance after the occurrence of variations, can provide a different perspective based more on the structural property itself. Although robustness has been mainly used in structural design optimization against progressive collapse and extreme events, it can also be used in assessing the condition of bridges with material deterioration. In this paper, a time-varying robustness index model is proposed to quantify the condition of the reinforced concrete bridge girder under corrosion. In this model, the robustness index represents the average performance of the concrete girder in the remaining life. The method is exemplified through a case study of an existing reinforced concrete bridge girder. Combining with the current specification, the robustness index is compared with the reliability analysis results of the girder in the case study. The result shows that when the reliability index drops below the target reliability index, the robustness index descends to Grade 5 specified in the Code for Maintenance of Highway Bridge and Culvers (JTG H11-2004). Both results indicate that the safety of the girder cannot satisfy demand.

Recent studies show that the evaluation of structures in the energy domain has attracted some researchers’ attention in the field of progressive collapse. Column buckling and failure energy were introduced as the energy-based criteria and can be obtained from the single-column displacement controlled analysis for progressive collapse assessment of steel structures. Accordingly, the structural performance following the columns removal scenarios can be evaluated by comparing the column’s internal energy to the energy criteria. In this paper, three-dimensional numerical simulations are conducted to investigate the buckling and post-buckling behavior of the box-section steel columns and derive the energy criteria. In addition to the simplified single-column model, to evaluate the role of beams on the derivation of the energy criteria, beams with different sections are explicitly considered in the finite element models according to the column location. The results show that the lack of explicit modeling of beams in the analysis, depending on the column’s permanent load, can lead to conservative and non-conservative results in deriving the energy-based criteria for progressive collapse assessment of steel structures.

Structural behavior of RC structures under explosive loads is an emerging field of research especially RC columns since the damage of RC columns can lead to progressive collapse. Most research works investigated and concentrated on the behavior of RC columns when exposed to far-field detonations (FFD). A limited study is available on the effects of near-field detonation (NFD) and close-in detonation (CID) on the behavior of RC columns. Hence, the main purpose of the current research is to investigate the influence of different types of detonation scenarios on the dynamic behavior of RC columns. The influences of extreme loading conditions on the columns are defined by using Lagrangian analyses in LS-DYNA. Validation of the numerical model is implemented by comparing the numerical analysis results with UFC 3–340-02 Standard. It is shown that the model yields a reliable prediction of damage on all RC columns. Intensive studies are performed to evaluate the influences of various scaled distances on the dynamic behavior of the columns. The results demonstrated that when the columns are subjected to CID explosions, they undergo the maximum pressure and the columns fail due to severe impulsive regime loading. The results revealed that when the scaled distance is in the CID range, the peak blast load increases but the duration of the positive phase of the blast wave decreases resulting in higher amplitude, lower-duration shock pulse and when the scaled distance is in the FFD range, the peak blast load decreases but the duration of the positive phase blast wave increases resulting in lower amplitude, longer-duration shock pulse. Also, the results show that increasing the scaled distance in RC columns subjected to NFD and FFD detonations resulted in a further decrease in the peak deflection histories and damage degree of RC columns in comparison to CID explosions. The current investigation and the outcomes can be utilized for evaluation of the effect of an explosion on the RC columns.

The progressive collapse resistance of reinforced concrete (RC) and precast concrete (PC) buildings has become a rising concern in recent years. Extensive research has been conducted to investigate the structural response of framed concrete structures after the local damage of single or multiple structural components. Being essential components in buildings, slabs play a crucial role in mitigating the progressive collapse of structures. This paper presents a comprehensive review of current research on the slab performance in RC and PC structures to resist progressive collapse. The structural resistance mechanisms exhibited by the slabs during a collapse event is discussed in detail. A database of experimental research on RC beam slab and RC flat plate substructures is collated and compared. Moreover, factors affecting progressive collapse resistance of RC structures, such as loading configurations, boundary conditions, reinforcement ratios, slab thickness and dynamic effects are discussed. The retrofitting techniques proposed in the literature to mitigate progressive collapse are also reviewed and some design proposals are suggested.

The progressive collapse of reinforced concrete structures usually starts as a local failure, which occurs because of abnormal loads. This can result in enormous economic losses and catastrophic extensive casualties. To avoid high costs of testing full-scale structures and save time, the implementation of the finite element method (FEM) is, therefore, inevitable. This paper aims to develop an FE model using ABAQUS software to simulate the progressive collapse phenomenon of reinforced rubberized concrete frames. The proposed numerical model is validated by comparing the FEM results with the experimental test observations. The numerical study is extended to include more ten models with different stories and details for further understanding of progressive collapse. Based on the results, the simulation model achieved good results compared to the experimental results. Moreover, the numerical models of full-scale frames satisfied the resistance requirements of progressive collapse according to the guidance.

An efficient and accurate beam element for performing explicit dynamic analysis of reinforced concrete beam elements was built using the absolute nodal coordinate formulation (ANCF). Such a formulation is useful for performing dynamic analysis under large strains and displacement with sudden load changes, such as during impact loading or for progressive collapse analysis. Compared with traditional nodal position formulations, ANCF uses position vector gradients to describe the rotation of the body and strain state, thereby avoiding the need for interpolating non-vectoral rotation parameters. The fiber element method was applied to calculate element stiffness from section deformations by subdividing beam elements into uniaxial fibers. The combined fiber element beam-column model with ANCF was validated by traditional co-rotational analysis and the quadrature element method (QEM), and thus may be used in general nonlinear dynamic analysis.

The progressive collapse method (PCM) in ship structures, in which local buckling is simplified by average compressive stress-strain curves of stiffened plates, is extended to analyze the ultimate bearing capacity of steel box girders for bridges. The PCM for steel bridges is reconstructed as the progressive-models method (PMM). Subsequently, a detailed PMM used for large-scale steel box girders is proposed and implemented through a two-stage analysis, which includes the nonlinear analysis of stiffened plate using shell finite element (FE) model and the nonlinear analysis of member using beam-column theory. The PMM is demonstrated by using an example tested steel box girder of which the ultimate bearing capacity is influenced by local buckling. The traditional finite element (FE) models of the tested steel box girder, including the refined shell FE model, beam-column FE model and multi-scale FE model, are established to make a comparison and validate the proposed method. The results show that the stability of each stiffened plate in the studied steel box girder is different, among them the mid web, of which the ultimate strength is 0.65 times of the yield strength at the severe defect level, is the most susceptible to buckling. Compared with results of the test and traditional FE models, the PMM is conservative for predicting the ultimate bearing capacity. In addition, the comparison of the scale of models shows that the PMM proposed can significantly reduce the complexity of modeling and improve the computational efficiency, thus the PMM has potential practical application value. The PMM can be regarded as a new attempt for the ultimate bearing capacity analysis of large-scale steel bridge members.

Removal of primary structural components such as columns from structures may rapidly result in a progressive collapse to trigger. While investigating the progressive collapse of structures has been a demanding subject for decades, rare studies have yet been performed on post-earthquake progressive collapse. This article investigates the possibility of progressive collapse in seismically designed steel structures under post-earthquake column removal scenarios. In this line, 14 structures with different stories, span number, span length, behavior factor, and seismic hazard levels are investigated. The cases studied are first controlled for column removal scenarios under only the gravity loads. The cases are then subjected to 12 seismic accelerations with different specifications followed by column removal scenarios in arbitrary locations. Results show that not all of the cases studied can keep their robustness when faced with such scenarios. The results show that two factors, behavior factor, and seismic specifications, can highly increase the possibility of post-earthquake progressive collapse. As well, the results show that upper stories are more vulnerable toward progressive collapse rather than the lower stories. It is concluded that designing structures for seismic loads cannot necessarily guarantee structural safety under the column removal scenarios, either under the gravity loads alone or under post-earthquakes. Therefore, mitigation strategies should be adopted in advance to increase the safety levels of structures when such scenarios are the case.

To study the effects of infill wall on progressive collapse resistance of reinforced concrete (RC) frames with slabs, a macro finite element (FE) model was built using general purpose software OpenSees. The FE model was validated by existing test results. Then, the model was subsequently used to predict the progressive collapse potential of eight-story RC frame including slabs and infill walls. The numerical studies demonstrated that the inclusion of the slabs and infill walls could increase the ultimate load and initial stiffness by 70% and 169%, respectively, compared with the bare frame. The infill walls not only changed the load resisting path but also effectively improved the load redistribution ability of the frame. To evaluate the reliability of using a two-story sub-structure to investigate the progressive collapse behavior of a multi-story building, the resistance of each story of a multi-story building in case of column missing is compared. It was found that the resistance of each story was similar, except the first story. Finally, a series of parameter studies were carried out to quantify the effects of opening ratio, thickness and compressive strength of the infill walls on the progressive collapse performance of RC frame.

This paper investigates the behaviour of two popular structural systems subjected to overheating and column removal cases, which may follow fire incidents. A typical 15–storey steel building is designed with two types of structural system framed-tube and moment-resisting frame. The nonlinear behaviour of these structures under different fire scenarios is investigated using OpenSees Software. The results indicate that deflection of heated beams is insignificant below 400 °C but after that, degrading mechanical properties of steel material leads to large deflection and runaway of heated beams at temperatures below 600 °C. Also, heating the beams of structures initially induces large axial forces in the beams due to restraints on thermal expansion. Thermal expansion of heated floors induces large horizontal displacement and consequently causes additional bending moments in the exterior column. So columns reach their elastic limit at the early stages of fire. Columns of the framed-tube system reach their elastic limit at lower temperatures (130 °C) but fail at higher temperatures (380 °C) compared to columns of the moment-resisting frame system (210 °C). In addition, the lower storey and interior columns are more vulnerable to progressive collapse and fail at lower temperatures (330 °C) due to carrying more gravity loads. In most fire scenarios, beams and columns of framed-tube systems fail at higher temperatures and perform well in the fire than moment-resisting frame systems. In column removal scenarios, mid-span displacement of the heated beam increases significantly, leading to downward movement of upper stories. Also, column removal in the framed-tube system is more destructive than in the moment-resisting frame system. In general, in both structural systems, column removal scenarios, which may follow fire, induce more damage to the structures than general temperature rise in considered fire scenarios.

The progressive collapse resistance of four full-scale special-shaped columns composed of concrete-filled steel tubes (S-CFST column)-steel beam assemblies was studied in this paper. The failure modes, deflection profiles, vertical resistance development mechanisms and internal force development at the assumed plastic hinge section under the influence of infilled concrete, various span-to-height ratios of the steel beam and different connection details were compared. The test results showed that the fracture failure of all the specimens first occurred near the full penetration weld of the bottom beam flange or the bottom cover plate at the end of the side plate. Fracture failure of the steel beam web or shear plate occurred through the bolt holes. The beam chord rotation ranged from 0.055 to 0.088. The concrete infilled steel tube improved the ductility of the assembly and resulted in the development of the catenary mechanism, while reducing the span-to-height ratio of the steel beam resulted in the delay of the initiation of the mixed mechanism stage. Additionally, the development of the catenary mechanism was more sufficient for the specimen with the concrete infilled steel tube than the specimen without the concrete infilled steel tube under the same vertical displacement. The results showed that the ACPSP connection can avoid premature fracture of the full penetration weld and improve its progressive collapse resistance. By reducing the span-to-height ratio of the steel beam and using the ACPSP connection, the beam-column assemblies experienced not only the flexural and mixed mechanism stages but also the catenary mechanism stage. The GSPCP connection was proposed to improve the stress concentration in the ACPSP connection. Through further analysis by the verified finite element model, it is evident that the GSPCP connection can further improve the progressive collapse resistance of the S-CFST column-steel beam joint assembly.

Many engineers are interested in the progressive collapse phenomenon, considering multi-user typical buildings, construction bias toward economization and thus, reduction of material consumption. The key factor in progressive collapse is the disproportion between the initial and final damage which sometimes can lead to the destruction of the whole building. So, the efforts are focused to prevent the expansion of initial damage through some strategies such as strengthening some load-bearing elements or choosing a proper plan. GSA and UFC regulations are two very reliable resources regarding the progressive collapse in which the alternative path method (APM) is one of the most common methods to evaluate building response to progressive collapse. In this study, the influence of typical concrete building plans (i.e. square and rectangular) on progressive collapse is investigated by 3D modeling of the buildings using LS-DYNA finite element software and removing a corner column using APM, considering GSA and UFC regulations. The results indicate that removing a corner column in the rectangular building has more intense effects including doubling the downward collapse rate, increasing the shear and axial loads in columns by 1.5 times, reciprocating motion of shear loads and higher energy absorption rate in comparison with those in the square building.

Controlled rocking steel cores (CRSCs) may suffer progressive collapse because of inadequate structural design and loss of re-centering action. While the CRSCs displace in the first-mode frequency, the demands of their members are strongly affected by higher modes. Conventional lateral load distributions, such as the uniform and inverted triangular, cannot predicate the design forces of CRSCs. This paper proposes new lateral loads for the design of CRSCs. Continuum cantilever beam analogy is utilized to formulate the higher-mode contribution. The application of the lateral loads is validated through illustrative examples of low- and mid-rise CRSCs. Results supported by nonlinear time response analyses demonstrate the effectiveness of proposed formulae for reliable estimation of seismic demands. The proposed lateral forces are readily applicable in commercial software without gap modeling at the base boundary conditions of CRSCs.

The progressive collapse of buildings may result in major financial losses and fatalities, so reducing the chances of such occurrences is of paramount importance. Due to the absence of beams for redistribution of gravity loads that were initially resisted by the missing column, flat slab buildings are more prone to progressive collapse than moment frame buildings. Thus, flat slab buildings should necessarily be assessed for progressive collapse and strengthened accordingly in order to avoid the likelihood of progressive collapse. This study evaluates the efficacy of three different strengthening methods for reducing the potential for progressive collapse of a validated 3-bay by 3-bay 4-storey flat slab building simulation model, subject to alternate, simultaneous and sequential removal of columns in the first storey. Corner, edge and interior columns of each building model are statically and instantaneously removed and the static and dynamic response of the building is compared for different removal sequences. The three strengthening strategies investigated are the addition of perimeter beams, the addition of shear walls and the addition of both perimeter beams and shear walls. The results are evaluated in terms of the vertical displacements at the top of the removed columns and the DCR of the sectional forces of critical adjacent columns, for which the acceptance criteria provided for DCR by the GSA is used to assess the vulnerability of the studied building to progressive collapse. The results show that perimeter beam, shear wall and combination of both perimeter beam and shear wall improve the progressive collapse resistance of the studied building by reducing DCR of critical columns by up to 67.0% and reducing the vertical displacements at top of the removed column by up to 81.0% depending on the different column removal cases.

Experiments were conducted to evaluate the progressive collapse resistance of a scaled partial double-layer latticed Kiewitt-6 (K6) dome in member-removal scenarios. The test results were compared with results obtained previously for a single-layer latticed dome to demonstrate the advantages of the partial double-layer members for improving the collapse resistance. A finite element (FE) analysis was also executed to confirm the experimental observations and to evaluate that the collapse-resistant behavior of a full-scale partial double-layer latticed dome. The collapse-resistant mechanism of partial double-layer domes was examined via theoretical analysis. On the basis of these results, a novel cable-stiffened partial double-layer latticed dome was proposed. The results indicated that the tested dome did not completely collapse, but some of the upper chord members buckled. For the whole dome, the compression mechanism is regarded as the major load-carrying mechanism to resist progressive collapse. In terms of the local area around the failed members, the adjacent members initially rely on the beam and compression mechanisms to resist progressive collapse. As the number of the failed members increases, the adjacent members completely rely on the beam mechanism to resist progressive collapse. The FE results agree well with the experimental results. The progressive collapse-resistant behavior of partial double-layer domes is far superior to that of single-layer domes because of the better stiffness of the partial double-layer members. The cable-reinforced partial double-layer dome is a novel structural system that has significantly better progressive collapse-resistant behavior than traditional single/double-layer and partial double-layer domes.

[EN] This study aimed to experimentally analyse the robustness of riveted steel bridges based on truss-type structures and to define practical recommendations for early detection of local failures before they cause progressive structural collapse. Although there are many experimental studies on robustness and progressive collapse on buildings, those on bridges are either theoretical or deal with actual collapses. This paper describes a unique case of a 21m full-scale bridge span tested under laboratory conditions with an extensive monitoring system, together with an experimental study to evaluate structural behaviour and robustness as damage or failure progressed in its elements. A linear-static finite-element analysis was also included to examine other possible causes not included in the experiment. The results proved the structural redundancy of this type of truss structure based on the joints¿ resistance to bending moments and gave rise to a series of practical structural health recommendations to identify early failures and avoid progressive or sudden bridge collapse. The study carried out and the recommendations it produced are now being applied in three similar bridge case studies., We would like to express our gratitude to the FGV (Ferrocarrils de la Generalitat Valenciana) and FCC Construcción S.A., CHM Obras e Infraestructuras S.A., Contratas y Ventas S.A. and CALSENS S.L. for giving us the opportunity to test a bridge at the ICITECH facilities, also to Juan Antonio García Cerezo, of FGV, for his invaluable cooperation and recommendations. We also wish to show our gratitude for the magnificent work on the bridge by Jesús Martínez, Eduardo Luengo and Daniel Tasquer. The tests on the bridge meant that much of the Structures Laboratory was out of service for other work, for which we owe a debt of gratitude to our ICITECH colleagues for their infinite patience and understanding.

This paper presents a comprehensive structural assessment of the fire-induced progressive collapse of Plasco Building, in January 2017. The assessment employs a three-phase approach: a) field investigation to collect data about the building and the event, b) structural evaluation against service loads, c) progressive collapse analysis. A collapse scenario is proposed, which is simulated using finite element modelling and numerical analysis. The results showed the adequacy of the building for service loads, while its significant vulnerability against progressive collapse. The vulnerability was mainly due to the lack of adequate continuity, ductility, and redundancy to resist the spread of damage. The weakest link in the structural system was the beam to column connections, which reached their critical temperatures first and failed to resist the local failure loads. Furthermore, exposure of unshielded structural components to the fire had led to a more severe condition, which eventually by the occurrence of failures over consecutive stories, buckling of the columns, and significant change in the geometric shape of the structure, the total collapse of the building occurred. The results of this investigation are considered as valuable tools for recognizing the deficiencies of the structural provisions in Iran against such events.

This paper investigates the influence of perforated masonry walls on the progressive collapse resistance of multi-story reinforced concrete (RC) structures. In this study, bare and infill-wall RC frames are studied by considering column failure at corner and exterior locations. Infill-wall panels are simulated by using equivalent compression struts and their provision of alternate load paths under the removal of a critical load-bearing element is examined. Linear static, nonlinear static, and nonlinear dynamic analyses are conducted by following the General Service Administration (GSA) guidelines. The analysis results show that the infill walls are beneficial in the redistribution of loads after the failure of the column and the collapse resistance of the RC building is increased. Empirical dynamic amplification factors (DAF) are also calculated in the sequel and the factor instructed in the GSA guidelines is judged by comparing with these computed dynamic factors. The results show that the DAF of 2, recommended by the GSA guidelines, is conservative and the presence of infill walls does not significantly affect the value of DAF.

Compressive arch action (CAA) is one of the favorable resistance mechanisms at low deflections against progressive collapse of reinforced concrete (RC) frame buildings. In this study, Park & Gamble model for calculating the CAA capacity of RC frame structures is modified by incorporating a compressive stress block for high strength concrete (HSC). Meanwhile, a comprehensive database of RC specimens is collated and the modified model is applied on the database to determine the peak deflection (δ) values at CAA by using an iterative approach. The δ values obtained are then modelled by using distinctive features of gene expression programming (GEP) to develop a relationship for δ as a function of height (h) and net span length of the two beams after the column removal (L). The proposed model is validated against a wide range of published results and compared with other models available in literature. The comparison shows that the proposed modified Park & Gamble model can accurately predict the CAA capacity of the specimens. Moreover, the developed model is easy-to-use and skips the oversimplified assumption proposed in the Park & Gamble model to calculate δ (i.e. δ = 0.5*depth of the specimen).

If unpredictable loads are applied to flat slab-column connections, punching shear failure occurs with almost no warning signs. To prevent progressive collapse of flat slab-column connections, it is necessary to provide a secondary load carrying mechanism after punching shear failure. In this research, some suggestions for establishing an alternative mechanism in flat slab connections after punching failure are proposed. For this purpose, an experimental program was conducted to investigate the post-punching behavior of 17 slabs with various reinforcement layouts and concrete covers. The effects of integrity, compressive, shear, truss, and bent-up reinforcements, diameter of tensile reinforcement, and concrete cover of tensile reinforcement on the post-punching behavior of slab-column connections were studied. The results of the experiments indicate that the integrity reinforcement significantly improves the post-punching strength. The increase of the concrete cover of the tensile reinforcement and decrease of the diameter of the tensile reinforcement result in an increase of the post-punching strength. Bent-up integrity reinforcement increases the punching and post-punching strengths, simultaneously. Truss reinforcement significantly improves the punching and post-punching behavior.

In this paper, macro-modeling methods of the slab-column connections were suggested to predict their post-punching behavior. These modeling techniques can be used to evaluate the potential for progressive collapse of flat slab buildings. It is acknowledged that structural damage is primarily focused on the flat slabs at their slab-column connections. In the suggested model, shell elements were used to simulate the plate and beam connector components to simulate punching failure. Six load-deformation curves were implemented with linear and nonlinear behaviors to simulate bending, shear, torsion, and axial force of the beam connector components to model the inner forces transfer between the slab and the column and to study the action of the connections. Two methods of macro modeling for simulating post-punching behavior were presented: rebar-modeling, link element modeling. The rebar or link element is placed vicinity to the connector beam element and activated after the punching failure. A bilinear load-deformation curve for the link element is defined to simulate post-punching behavior. Some of the parameters used to introduce these curves are calibrated with the test results. Test specimens validated the proposed methods. The results show that both post-punching behavior modeling techniques have acceptable accuracy in predicting post-punching strength, post-punching stiffness, and deformation capacity.

In recent years, the interest in knowledge and evaluation of the post-critical path of structures has increased mainly due to the recent occurrence of terrorist attacks and other exceptional events. In steel structures, joints play an essential role in the structural behaviour. Therefore, an adequate resistance is vital to prevent progressive collapse. This study presents a numerical evaluation of steel structures with bolted flush endplate semi-rigid joints using models based on finite element method focused on their post-critical nonlinear response. The current investigation addresses the structural behaviour of steel joints centred on the collapse of an internal column scenario. Furthermore, the structure robustness and the steel joints structural response was evaluated, as well as the development of internal stresses. The results were also estimated and compared with the main robustness design codes. The results indicated that the presence of elements able to withstand substantial tension loads is conditioned to an increase of the structural robustness to prevent progressive collapse. Within this perspective, the results also indicated that an increase of the bolt diameter led to an enhanced rotation capacity and ability to sustain gravity loads. Besides, it was noticed that most of the evaluated joints were able to meet the codes criteria to prevent progressive structural collapses.

The sudden rupture of cable is one of the factors that can threaten the bridge safety; causing progressive collapse due to severe vibrations along with numerous changes in the internal forces of all bridge members. Therefore, analyzing the bridge behavior after the sudden cable rupture and estimating the maximum response of the bridge members is of great importance. According to Post-Tensioning Institute (PTI), the sum of the static analysis responses of two models can be used instead of dynamic analysis of cable rupture. In one of these models, the ruptured cable should be removed and twice its tensile force should be applied at the two ends of the cable. In this study, an approach proposed for investigating the tensile force coefficient (TFC) of the ruptured cable in the model of cable rupture effect. For this purpose, an optimization problem was defined to minimize the difference between the static and the maximum dynamic analysis results. The performance of the proposed approach is illustrated with a three-span cable-stayed bridge. This problem was solved for the rupture of each of the bridge cables under examination at different durations of cable rupture using ECBO meta-heuristic algorithm. Moreover, this meta-heuristic algorithm was used to adjust the tensile forces of the cables. Based on the results, a general form of equations was found between cable rupture duration and TFC, which the maximum of it, is in accordance with the PTI coefficient. According to this equation, increasing the cable rupture duration reduces this coefficient.

Post-tensioned energy-dissipating (PTED) connections for steel frames have drawn great research attention on account of their good seismic performance. Few studies focus on the progressive collapse of friction damped post-tensioned (FDPT) frame structures. The progressive collapse of FDPT frames exhibits a complex three-dimensional mechanical behavior that is quite different from that of traditional frame structures. In this work, a simplified 3D PTED connection model was first established and then used to investigate the progressive collapse behavior of FDPT frames. The influences of material strength, initial PT force, friction force, and axial and bending stiffness of beams on the collapse behavior of FDPT were studied. Finally, the dynamic response of FDPT frames was compared with that of traditional frame structures (TF).

In order to develop super long-span structures, the characteristics of suspension bridges are considered for use in suspended hybrid structures, initially considering a structure with a span of 800 m. The control parameters for the geometrical shape of the structure are given, and a structural model is established using ANSYS. The initial form of the main cable is studied and a feasible pylon scheme is designed. Static, stability and parameter analysis of the structure are conducted, and progressive collapse analysis after the breakage of the sling is undertaken. The results show that both wind loads and temperature have significant effects on the structure. There is not a destabilization problem exist in the structure and stiffness should be taken as the main consideration. The influence of geometrical parameters on the mechanical properties of the structure is studied, and variation rules for the parameters are summarized. The rise-span ratio of has a great influence on structural performance. When it changes from 1/10 to 1/5, the displacement decreases by 43%, the steel consumption reduces by 8.86%, and the stress decreases by about 10.69%. The possible progressive collapse of the structure following the failure of a single sling is examined. Using transient dynamic analysis. The time history curves of the responses to the process of the breakage of the sling are given. The work shows that it should be possible to develop suspended mega-latticed structures with spans of 800 m.

Catenary action provides more resistance to progressive collapse of semi-rigid jointed steel frames in spite of the axial tension force developed in catenary action stage reduces the moment capacity of the connection. Dual effect of axial tension and its impact on the global structure response is not investigated yet. Limited works have been carried out on beam-column sub-assemblages. This paper studies the dual effect of axial tension developed during catenary action stage of a 3D composite multi-story building with TSD connection taking into account both material and geometry nonlinearity. ND progressive collapse analysis is carried out following the APM recommended by DoD using ABAQUS software. The results show that axial tension improves the progressive collapse resistance by 23% to 36% depending on the column removal locations whereas, the building response increases by 18% to 35% when the connection moment capacity is reduced due to the axial tension. Thus, the designers and engineers have to be cautious while depending on only the positive influence of axial tension developed in the catenary action stage because it simultaneously reduces the connection moment capacity which causes some negative effect on progressive collapse resistance. Also, this study presents a suitable and economical retrofitting scheme by providing bracing on the top floor which enhances the progressive collapse resistance.