Model updating-based dynamic collapse analysis of a RC cable-stayed bridge under earthquakes

Shaking table test for assessing the seismic performance of semi-anchored steel water tanks

Progressive collapse is defined as the spread of an initial local failure of a critical load bearing structural element to the remaining structure, ultimately leading to the collapse of the entire building or of a large portion of it. After the partial collapse of the Ronan Point apartment tower in 1968, when a localised gas explosion ultimately led to the collapse of the whole corner of the building, progressive collapse firstly drew public attention due to its catastrophic consequences on human casualties and economic losses. Other recent collapse events, such as those of the Murrah Federal Building in 1995, Sampoong department store in 1995 and World Trade Centre towers in 2001, have further highlighted the importance of this topic and made engineering communities aware of the necessity to prevent the occurrence of progressive collapse in building structures. In the past decades, considerable research has been devoted to investigate progressive collapse of building structures. These research typically followed an alternate load path approach. This approach allows an initial failure to occur, while the remaining structure needs to seek alternate load paths to dissipate damage and prevent progressive collapse. In practice, the progressive collapse resistance of building structures is generally evaluated by notionally removing one or more load bearing structural elements, representing the initial failure. Despite all research efforts made, they have predominately focused on frame systems. Relevant investigations on reinforced concrete (RC) flat plate structures, a commonly used structural system, are still scarce. The flat plate system contains slabs, of uniform thickness, directly supported by columns without using beams, drop panels and column capitals. This provides structures with increased storey height, architectural convenience and significant savings in construction costs. Nevertheless, the slab-column connection is prone to punching shear failure, which may propagate to the vicinity of connections, potentially leading to progressive collapse. The present study aims at filling some of the current knowledge gap with comprehensive experimental, analytical and numerical investigations on RC flat plate structures. The experimental program consists of four quasi-static large-deformation tests performed on three 1/3-scale, 2×2-bay RC flat plate substructures subjected to critical column removal scenarios. The test specimens included one specimen tested under two consecutive corner column removal scenarios, one specimen under an edge column removal and one specimen under the scenario of concurrently removing both an edge and an interior column. For the loading scheme, a multi-point loading system was specially designed to simulate an increasing uniformly distributed load (UDL). The loading points of this system were equally positioned on the bays adjacent to the removed column(s) to apply the load until failure of the slab. Throughout each test, the structural behaviour of the slab was monitored by extensive apparatuses mounted to the slab both internally and externally. Failure and post-failure behaviours, failure modes, and collapse resisting mechanisms were observed and analysed. Additionally, a complement of analytical studies to the experimental tests, based on the observed yield lines, was carried out to estimate the flexural capacity of the test specimens. To numerically investigate the progressive collapse behaviour of RC flat plate structures, a set of 3D nonlinear finite element modelling approaches, using LS-DYNA software, was established. A total of five numerical models were explicitly created based on the four experimental tests in present research and one from the literature. The proposed modelling approach was basically composed of appropriate definitions of element types, bond-slip relationships, loadings and boundary conditions, and more importantly development of the material models for concrete and reinforcements and calibration of failure criteria for element erosion. A quasi-static loading scheme in displacement control in the numerical models was adopted, the same as that in the conducted tests, through explicitly modelling the multi-point loading system in order to replicate the true test conditions. The numerical models were respectively validated by comparing the load displacement responses, failure modes, crack patterns, and displacement and strain results against the experimental ones, which confirmed the appropriateness and reliability of the proposed models. The validated modelling techniques could be applied to further perform parametric studies of the progressive collapse resistance of RC flat plate substructures and prototype structures. In summary, the significant and original contribution of this research is to (1) obtain a solid understanding of the collapse behaviour of RC flat plate structures under critical column removal scenarios, (2) examine the analytical solution using the yield line theory to predict the flexural capacity of RC flat plate structures, (3) establish a set of numerical modelling techniques which can reasonably replicate the experimental process and provide valuable references of numerically analysing progressive collapse of RC flat plate structures, and (4) give design insights into Australian and international Standards in mitigating progressive collapse of RC flat plate structures.

This study involves the development of three-dimensional nonlinear Finite Element (FE) models of strengthened Reinforced Concrete (RC) beams with different anchorage systems, obtained from experimental testing. The aim of this investigation was to simulate the flexural behavior of strengthened RC beam, and compare FE and experimental results using load deflection response plots, maximum attained loads, and corresponding deflections. Three FE models were developed, which include: a reference RC beam, beam externally bonded (EB) with Aluminum Alloy (AA) plate along the soffit of the beam, and another strengthened beam with an AA plate EB to the soffit of the beam and anchored at its ends using Carbon Fiber Reinforced Polymers (CFRP) U-wraps. The developed FE models integrated nonlinear material properties and fundamental constitutive laws. The results obtained from the FE models closely agreed with those obtained from the experiment. Therefore, successful FE modeling has proven to provide great insight on the flexural behavior strengthened RC specimens. The performance of AA plated beams would be used as a valid platform to study the effect of different variables.

This study proposes a generally applicable improvement strategy for metaheuristic algorithms, improving the algorithm’s accuracy and local convergence in finite element (FE) model updating. Based on the idea of “survival of the fittest” in biological evolution, the improvement strategy introduces random crossover and mutation operators into metaheuristic algorithms to improve the accuracy and stability of the solution. The effectiveness of the improvement strategy with three typical metaheuristic algorithms was comprehensively tested by benchmark functions and numerical simulations of a space truss structure. Meanwhile, the initial FE model of a railway hybrid girder cable-stayed bridge was updated to examine the effect of the improved metaheuristic algorithm within the FE model, updating for complex engineering structures. The results show that the accuracy and stability of the improved metaheuristic algorithm were improved by this process. After the initial FE model of the hybrid girder cable-stayed bridge was updated, the calculated frequencies and displacements were closer to the measured values, better representing the actual structure, and showing that this process can be used for baseline FE models of bridges.

High strength reinforced concrete (HSRC) has been used more frequently in the construction of high rise buildings and other concrete structures in recent decades due to its advantages and excellent performance over normal strength and conventional reinforced concrete. Some of these advantages include: higher strength, better durability and allowance for provision of using less concrete and smaller section sizes. Although HSRC performs better than normal strength reinforced concrete (NSRC) at ambient temperatures, NSRC has been found to perform better than HSRC at elevated temperatures and fire conditions. Provision of adequate fire resistance for reinforced concrete (RC) structures is essential as fire represents an extreme loading and hazardous condition to which a structure might be exposed during its life span. The fire resistance of RC members is evaluated using a prescriptive approach which is irrational and conservative. Current codes of practice and construction in industry are moving towards performance based fire design method with computing software, which is a rationally based method with each structure designed to meets its own need. This method requires comprehensive knowledge and modelling of concrete and reinforcement material behaviour and their response at elevated temperatures. The fire resistance of HSRC members (columns and beams) in this study was evaluated using a three-dimensional Finite Element (FE) model created in ANSYS. The stress – strain behaviour of concrete proposed in this research was used in modelling the behaviour of concrete in ANSYS, while other concrete and steel material properties were accounted for by using models proposed by other researchers. The fire resistance of the HSRC members is evaluated using coupled field analysis (thermal – structural analysis) with performance based failure criteria provided in the code of practice. The accuracy of the FE model was verified by comparing the thermal response, structural response and predicted fire resistance with fire test results obtained. Using the validated FE model, parametric studies were conducted to investigate the influence of various parameters affecting the fire performance of HSRC members exposed to fire. From the parametric studies conducted, simplified calculation models were developed for evaluating the resistance of HSRC members (columns and beams) exposed to fire. These models were validated with results from ANSYS and a fire resistance test. The simple model accounts for major factors such as member size, load ratio and fire scenario, and therefore can be easily incorporated into structural design. The FE model and simple calculation model provide a rational approach for evaluating the fire resistance of HSRC (members) and predict a more accurate fire resistance than the prescriptive approach.

While linear finite element (FE) model updating has been successfully applied for predicting structural damage as loss of effective stiffness, nonlinear FE model updating can provide improved and more accurate damage identification (i.e., a more comprehensive measure of damage) and can additionally be used as a tool for damage prognosis. The current study is focused on characterizing the nonlinear material behavior in a FE model of a three-story infilled frame using the identified instantaneous natural frequencies and mode shapes. The 2/3-scale, 3-story, 2-bay reinforced concrete frame with masonry infills was subjected to large amplitude earthquake base excitations on a shake table. The deterministic stochastic subspace identification method is used for estimating the instantaneous (during short-time windows) modal parameters of the structure based on the nonlinear response of structure during a seismic base excitation. Parameters of a priori selected hysteretic models (Bouc-Wen) at different finite elements of the structural model are calibrated to minimize the misfit between the identified modal parameters and those from the FE model. The accuracy of the calibrated FE model is assessed through the comparison of the predicted response and natural frequencies obtained from the model with those of the specimen.

An efficient method for constructing multiple candidate finite element (FE) models which are consistent with the measured dynamic properties of a civil structure is presented. A parameterised sensitivity-based FE model updating method was developed to permit a feasible FE model set for the target structure to be produced. In this method, an aggregated multi-objective function, which is defined by the weighted sum of the error functions, is parameterised by its relative weighting factors. By introducing multiple parameter sets for the weighting factors, a number of optimal updated FE models are produced that permit both the natural frequency errors and mode shape errors to be simultaneously minimised. The effectiveness of the proposed method is illustrated by an example using an existing cable-stayed bridge. The findings show that error-minimised, well-distributed FE models can be obtained in terms of modal frequency errors and mode shape errors. The high quality of the candidate model sets is also verified by observations showing that the distributions of the structural parameters are consistent through each updated FE models, and the characteristic features of the target structure such as non-symmetric mode shapes are relatively well captured.

In this paper, a finite element (FE) model for a cable-stayed bridge designed according to Australian standards is developed and analysed statically and dynamically with and without geometrical nonlinearities. The dynamic amplification factor ( DAF) and demand-to-capacity ratio ( DCR) in different structural components including cables, towers and the deck are calculated and it is shown that DCR usually remains below one (no material nonlinearity occurs) in the scenarios studied for the bridge under investigation, however, DAF can take values larger than two. Moreover, effects of location, duration and number of cable(s) loss as well as effect of damping level on the progressive collapse resistance of the bridge are studied and importance of each factor on the potential progressive collapse response of the bridgeis investigated.

Assessment and mitigation on near-fault earthquake wave effects on seismic responses and pile-soil interactions of soil-pile-bridge model

The expansive polystyrene granule cement (EPSC) latticed concrete wall is a new type of energy-saving wall material with load-bearing, insulation, fireproof, and environmental protection characteristics. A series of shaking table tests were performed to investigate the seismic behavior of a full-scale reinforced concrete (RC) frame with EPSC latticed concrete infill wall, and data obtained from the shaking table test were analyzed. The experimental results indicate that the designed RC frame with EPSC latticed concrete infill wall has satisfactory seismic performance subjected to earthquakes, and the seismic responses of the model structure are more sensitive to input motions with more high frequency components and long duration. The EPSC latticed concrete infill wall provided high lateral stiffness so that the walls can be equivalent to a RC shear wall. The horizontal and vertical rebar, arranged in the concrete lattice beam and column, could effectively restrain the latticed concrete infill wall and RC frame. To achieve a more comprehensive evaluation on the performance of the RC frame with latticed concrete infill walls, further research on its seismic responses is expected by comparing with conventional infill walls and nonlinear analytical method.

Numerical investigation on progressive collapse resistance of post-tensioned precast concrete beam-column assemblies under a column-loss scenario

This study investigates the structural performance of Ultra-High-Performance Reinforced Concrete (UHPRC) rectangular columns under axial, uniaxial, and biaxial loading, with a focus on enhancing strength, ductility, and durability for modern construction. Eighteen columns were fabricated using three concrete grades (M60, M70, M80) and three reinforcement ratios (1.34%, 2.09%, 3.01%), and tested in a 2000 kN capacity loading frame. The effects of material strength, reinforcement content, and load type on load-carrying capacity and failure behavior were systematically assessed. Finite Element (FE) models, comprising 2D plane stress and 3D simulations, were developed and calibrated against experimental results, enabling accurate prediction of peak load, crack propagation, and post-cracking response. Experimental outcomes revealed that higher-grade UHPRC and greater reinforcement ratios substantially improved peak load capacity, post-peak ductility, and energy absorption across all loading conditions. Failure modes displayed gradual post-cracking behavior, highlighting enhanced structural resilience. An analytical load–moment interaction model was formulated and validated with close agreement to experimental and FE findings. The results confirm UHPRC’s potential for high-performance structural applications, providing valuable insights for designing strong, ductile, and durable rectangular columns in advanced engineering practice. Keywords: Ultra-High-Performance Reinforced Concrete, rectangular columns, finite element modeling, axial loading, uniaxial bending, biaxial bending.

Behavior of unbonded prestressed concrete slabs subjected to low-velocity impact loading

Static and dynamic FE analysis of an RC protective structure dedicated to snow avalanche mitigation

Experimental study on the collapse-resistant performance of unbonded prestressed PC beam-column sub-assemblages with pinned connections