In contemporary society, industrialization and rising of terrorism threats highlight the necessity and importance of structural protection against accidental and intentionally malicious blast loads. Consequences of these extreme loading events are known to be catastrophic, involving personnel injuries and fatalities, economic loss and immeasurable social disruption. These impacts are generated not only from direct explosion effects, that is, blast overpressure and primary or secondary fragments, but also from the indirect effects such as structural collapse. The latter one is known to be more critical leading to massive losses. It is therefore imperative to enlighten our structural engineers and policy regulators when designing modern structures. Towards a better protection of concrete structures, efforts have been devoted to understanding properties of construction materials and responses of structures subjected to blast loads. Reliable blast resistance design requires a comprehensive knowledge of blast loading characteristics, dynamic material properties and dynamic response predictions of structures. This article presents a state-of-the-art review of the current blast-resistant design and analysis of concrete structures subjected to blast loads. The blast load estimation, design considerations and approaches, dynamic material properties at high strain rate, testing methods and numerical simulation tools and methods are considered and reviewed. Discussions on the accuracies and advantages of these current approaches and suggestions on possible improvements are also made.
This article presents a finite element investigation into the web crippling strength of cold-formed stainless-steel lipped channels with circular web perforations under end-two-flange loading. The cases of web openings located both centred and offset to the load bearing plates are considered. In order to take into account the influence of the circular web openings, a parametric study involving 2190 finite element analyses was performed, covering duplex EN 1.4462, austenitic EN 1.4404 and ferritic EN 1.4003 stainless-steel grades; from the results of the parametric study, strength reduction factor equations are determined. The strength reduction factor equations are first compared to equations recently proposed for cold-formed carbon-steel lipped channels. It is demonstrated that the strength reduction factor equations proposed for cold-formed carbon steel are conservative for the stainless-steel grades by up to 10%. New coefficients for web crippling strength reduction factor equations are then proposed that can be applied to all three stainless-steel grades.
This paper discusses the application of Unmanned Aerial Vehicles (UAV) for visual inspection and damage detection on civil structures. The quality of photos and videos taken by using such airborne vehicles is strongly influenced by numerous parameters such as lighting conditions, distance to the object and vehicle motion induced by environmental effects. Whilst such devices feature highly sophisticated sensors and control algorithms, specifically the effects of fluctuating wind speeds and directions affect the vehicle motion. The nature of vehicle movements during photo and video acquisition in turn affect the quality of the data and hence the degree to which damages can be identified. This paper discusses the properties of such flight systems, the factors influencing their movements and the resulting photo quality. Based on the processed data logged by the high precision sensors on the UAV the influences are studied and a method is shown by which the damage assessment quality may be quantified.
The use of the vehicle-bridge interaction (VBI) data for structural health monitoring has received considerable interest in the last decade. Compared with the traditional bridge health monitoring, the VBI based approach allows the target bridges to be monitored or assessed under operating conditions. The VBI system has time-variant features and the vehicle can serve as a moving exciter and a mobile sensor in the system. Many bridge damage identification techniques based on VBI have been developed, and they could be divided into three categories, namely, technique based on the bridge responses, technique based on the vehicle responses and technique based on both the vehicle and bridge responses. This paper presents a review on the structural health monitoring based on VBI and the challenges for its general implementation in practice.
As China’s infrastructure grows rapidly, the use of concrete-filled steel tubular structures for engineering applications is attracting increasing interest owing to their high section modulus, high strength and good seismic performance. However, for concrete-filled steel tubular members with large width-to-thickness ratio, steel tubes are prone to outward buckling when they are subjected to axial compression. Welding of longitudinal stiffeners on the steel tubes is one of the most efficient approaches for delaying local buckling and thus improving the mechanical performance of such type of concrete-filled steel tubular members. This study attempts to investigate the axial compression behaviour of concrete-filled stiffened steel tubular members with square sections through experimental study and finite element analysis. First, 14 concrete-filled steel tubular stub columns, with different width-to-thickness ratios of steel tube and depth-to-thickness ratios of stiffener, were subjected to axial compression loads and tested. It was found that the use of stiffeners increases the ultimate strength and improves the stability of the stub columns. Later, an investigation on the behaviour of the stiffened concrete-filled steel tubular stub columns was carried out through a three-dimensional finite element analysis. The accuracy of the finite element analysis model was verified by the test results. A parametric study was conducted to further evaluate the stiffening schemes that influence the axial compression strength. Finally, the research findings were synthesized into a new simplified model to predict the load-carrying capacity of stiffened concrete-filled steel tubular stub columns that allows for large width-to-thickness ratios.
This article presents a numerical investigation on the web crippling strength of cold-formed stainless steel lipped channel sections with circular web openings under end-one-flange loading condition. In order to take into account the influence of the circular web openings, a parametric study involving 1992 finite element analyses was performed, covering duplex EN1.4462, austenitic EN1.4404 and ferritic EN1.4003 stainless steel grades; from the results of the parametric study, strength reduction factor equations are proposed. The web crippling strengths predicted by the reduction factor equations are first compared to the strengths calculated using the equations recently proposed for cold-formed carbon steel lipped channel sections. It is demonstrated that the strength reduction factor equations proposed for cold-formed carbon steel are unconservative for the stainless steel grades by up to 7%. Unified strength reduction factor equations are then proposed that can be applied to all three stainless steel grades.
Fire loading following earthquake loading is possible in any building in a seismic-prone area. However, most design approaches do not consider fire following earthquake as a specific loading case. Moreover, seismic design philosophies allow a certain degree of damage in structural elements which make structures more vulnerable when subjected to post-earthquake fire. This study uses three-dimensional numerical models to investigate the effect of earthquake damage on the fire resistance of composite steel-frame office buildings. A total of two types of earthquake damage, fire insulation delamination and residual lateral frame deformation, are investigated. It is concluded that earthquake damage can significantly reduce the fire resistance of composite buildings, with delamination of fire protection having the greatest effect. The results of this study can be used by designers to improve the post-earthquake fire resistance of composite buildings.
To improve the efficiency of reliability calculations for vehicle-bridge systems, we present a surrogate modeling method based on a nonlinear autoregressive with exogenous input artificial neural network model and an important sample, which can forecast responses of dynamic systems, such as vehicle-bridge systems, subjected to stochastic excitations. We also propose a process to analyze the method. A quarter-vehicle model is used to verify the proposed method’s precision, and the nonlinear autoregressive with exogenous input artificial neural network model is used to predict responses of vertical vehicle-bridge systems. The results show that, compared to other training samples, the nonlinear autoregressive with exogenous input artificial neural network model has better prediction accuracy when the sample with the maximum response is considered as an important sample and is used to train the nonlinear autoregressive with exogenous input artificial neural network model, and it requires only two-time numerical simulation (or Monte Carlo simulation) at most, which is used in the training of the nonlinear autoregressive with exogenous input artificial neural network model.
This article introduces and evaluates the piecewise polynomial truncated singular value decomposition algorithm toward an effective use for moving force identification. Suffering from numerical non-uniqueness and noise disturbance, the moving force identification is known to be associated with ill-posedness. An important method for solving this problem is the truncated singular value decomposition algorithm, but the truncated small singular values removed by truncated singular value decomposition may contain some useful information. The piecewise polynomial truncated singular value decomposition algorithm extracts the useful responses from truncated small singular values and superposes it into the solution of truncated singular value decomposition, which can be useful in moving force identification. In this article, a comprehensive numerical simulation is set up to evaluate piecewise polynomial truncated singular value decomposition, and compare this technique against truncated singular value decomposition and singular value decomposition. Numerically simulated data are processed to validate the novel method, which show that regularization matrix L and truncating point k are the two most important governing factors affecting identification accuracy and ill-posedness immunity of piecewise polynomial truncated singular value decomposition.
The hanger arrangement has a decisive influence on the mechanical behavior of the tied arch bridge with network hanger system. Many investigations on highway or railway tied arch bridges show that the arch bridges with dense network hangers are superior to those with vertical hangers under larger live load. However, numerous dense inclined hangers lower the esthetic effect of the bridge, especially for pedestrian tied arch bridges. Consequently, the sparse inclined hanger system is recommended in the design of pedestrian tied arch bridges. However, the amount of possible schemes of the hanger arrangement grows rapidly with the number of hangers increasing beyond 10, rendering great difficulties in searching for proper schemes. In this article, a dimensionless optimization approach based on genetic algorithm is proposed in searching for hanger arrangement schemes. Numerical analysis indicates that the proposed method is effective in the optimization of pedestrian tied arch bridge with sparse inclined hanger system, and some of the feasible hanger arrangement solutions show more excellent mechanical properties.
A novel precast concrete beam–column connection locally post-tensioned using arc-shaped prestressing bars was proposed for satisfactory seismic performance and rapid construction. Three full-scale cruciform specimens, including one monolithic reference specimen, were tested under reversal cyclic loadings to evaluate the seismic behaviours. Grade 630 steel rods and high-strength deformed steel rebars were used for the arc-shaped prestressing bars in the precast specimens. The results show that the proposed precast connection presents an acceptable seismic performance and that the structural details should be ameliorated to improve the energy dissipation capacity. The design philosophy of strong column-weak beam is applicable to the new precast system. Finally, a strut-and-tie model was developed to investigate the force transfer mechanism of the novel precast connection.
An assembling method of precast shear walls was previously proposed using steel–concrete composite bolted connectors. To further investigate the effectiveness and mechanical behavior of the proposed composite connector, 11 specimens were fabricated and tested under monotonic tensile loading. The test results provided comprehensive data (e.g. load, deformation, failure mode) on the effects of variation in the thickness of steel cap plate, concrete strength, bolt tension, and bolt diameter. Two typical failure modes were observed in the test: bearing failure and bolt shear failure. Finally, the equations for calculating the ultimate strength and yield strength of steel–concrete composite bolted connector are proposed in this article by reference to those of conventional bolted connection. The proposed calculations are demonstrated to be accurate enough through verification with the experimental data.
The ability of an idealized piecewise-linear restoring force model and a nonlinear mechanical model to describe the hysteretic performances of the pre-pressed spring self-centering energy dissipation braces was evaluated based on experimental data. The hysteretic behaviors predicted by these two proposed models were compared with the experimental results of a typical prototype brace, and the results demonstrated that the two models can explain the brace force-time responses, and that the nonlinear mechanical model is more effective in describing the stiffness transition and energy dissipation of the brace. The two proposed models can be used for the design of the pre-pressed spring self-centering energy dissipation brace specimens, and the nonlinear mechanical model may be more useful for designing the structures with the pre-pressed spring self-centering energy dissipation braces. An orthogonal experiment was applied to analyze the influences of the key parameters on the performances of pre-pressed spring self-centering energy dissipation braces based on the nonlinear mechanical model. The results indicate that the friction slip force of energy dissipation mechanism, the pre-pressed force of self-centering mechanism, and the post-activation stiffness significantly affect the hysteretic performances and equivalent viscous damping ratios of the bracing system, while the changes in other parameters only produce slight effects. The determination of the pre-pressed force of the self-centering mechanism should be coordinated with the friction slip force of the energy dissipation mechanism to achieve a better hysteretic performance of the pre-pressed spring self-centering energy dissipation brace.
Corrosion of bridge pier columns in saline soil environment is inevitable, resulting in a gradual decrease in seismic yield displacement. In this study, 10 reinforced concrete bridge pier columns were fabricated, and seismic yield displacement in the saline soil environment was studied. Electrochemical corrosion tests and low-cycle repeated loading tests were carried out. The axial compression ratio and corrosion rate are the main parameters considered in this article. The seismic yield displacement test value of the pier column is determined based on the energy method. Using the static method, the theoretical expression of the earthquake yield displacement is derived. According to our results, when the corrosion rate is constant, the axial compression ratio is within a certain range, and the seismic yield displacement of the pier increases with the increase in the axial compression ratio. Similarly, when the axial compression ratio is constant, the seismic yield displacement decreases as the corrosion rate increases. By comparing experimental results with calculation results, our mathematical expressions have been shown to be effective in predicting seismic yield displacements of pier columns at different times in saline soil environments.
A series of tests were carried out on a scaled (1:8) double-deck prestressed concrete box girder in this study, aiming to study the structural response and failure mechanism of the box girder under prestressed axial compression, transverse bending, and torsion. The test results, such as the twist angle, crack development, and distortion of the box girder, were analyzed in detail. The results show that (1) the box girder eventually suffered lateral bending damage, and the cross-section of the support distorted severely; (2) torsional cracking occurred in the pure torsion region at the mid-span, but the longitudinal and transverse rebars did not yield, indicating that the pure torsion section of the box girder was still in the early stage of torsion failure; and (3) after the cracking of the box girder, stress redistribution phenomenon occurred, resulting in obvious nonlinear strain variations. Comparison of the longitudinal and transverse steel strains showed that transverse steel withstood the most shear stress during the early stage of torsion.
The failure behavior of a reinforced concrete corbel is complicated due to the shear span-to-effective depth ratio, reinforcement patterns, load conditions, and material properties. In this study, an optimum first-order indeterminate strut-and-tie model that reflects all characteristics of the failure behavior is proposed for the rational design of reinforced concrete corbels with a shear span-to-effective depth ratio of less than 1.0. A load distribution ratio that transforms the indeterminate strut-and-tie model into a determinate model is also developed to help structural designers design reinforced concrete corbels using the strut-and-tie model methods of current design codes. For the development of the load distribution ratio, a material nonlinear finite element analysis of the proposed first-order indeterminate strut-and-tie model was conducted repeatedly by changing the combination of primary design variables of the corbels. To examine the validity of our results, the ultimate strengths of 294 reinforced concrete corbels tested to failure by other investigators were predicted using the proposed strut-and-tie model with the load distribution ratio, the existing determinate strut-and-tie models representing arch and truss load transfer mechanisms, and the American Concrete Institute 318 conventional design method based on a shear friction theory. The ultimate strengths predicted by the proposed strut-and-tie model agreed fairly well with the experimental results. The ratio of the experimental strength to the predicted strength (and coefficient of variation) was 1.09 (28.0%), implying that the proposed strut-and-tie model can represent the load transfer mechanisms of corbels most appropriately.
This article proposes a new connection between a steel bearing and a reinforced concrete column, which is mainly used for provisionally providing jack support in existing reinforced concrete structures. In this suggested connection joint, the steel bearing consisted of two or four symmetrical components assembled by high-strength bolts, which surrounds the reinforced concrete column by a tapered tube and balances the vertical load via the friction force between the tapered tube and concrete, that is, through a self-locking mechanism. The proposed connection joint can be assembled easily at a construction site and can also be disassembled and reused many times. To demonstrate the feasibility of this type of connection joint, a simple test was conducted to illustrate the concept, that is, a total of four medium-scale steel bearing–reinforced concrete column connections with circular cross sections were fabricated and tested under axial loading. The test results showed that the steel bearing–reinforced concrete column connection based on self-locking mechanism exhibited good working performance. Furthermore, a simplified formula to predict the axial stiffness of the connection joint was presented. From the tests and the proposed formula, the most important factors that influence the axial stiffness of this type of connection joint on the premise of an elastic working state are the slope of the tapered tube, the height of the steel bearing, the thickness of the tapered tube, the cross section of the reinforced concrete column, the cross-sectional area of all the connecting bolts, the proportion of the number of top bolts, the area of the top ring plate, and the effective contact area ratio.
In this article, the optimum performance-based seismic design of steel frames is performed using the novel constraint control method. This method is based on a simple concept generally used by the engineers in structural design. In this method, the most conservative member sections are initially selected and by gradually reducing the size of the sections through controlling the problem constraints, the solution tends to an optimum design. The capacity curve of the structure is evaluated through static nonlinear analysis and used for the seismic assessment, and the structural weight is optimized by controlling relative displacement constraints at performance levels of operational, immediate occupancy, life safety and collapse prevention. The performance and efficiency of the proposed algorithm in solving for optimum performance-based seismic design are assessed through solving three benchmark problems. The results show that using constraint control method drastically reduces the number of structural analyses required to reach a solution, compared to the more commonly used metaheuristic optimization methods, while producing comparable optimum solutions. For this reason, the constraint control method is found to be particularly suitable as an optimizer for solving solution-extensive problems, such as performance-based optimum design of structures.
Ice force is one kind of nonnegligible external loads that nature exerts on structures. The action of drifting ice floes may induce strong vibrations of offshore structures, and further reduce the structural safety and serviceability. The aim of this article is to develop a method to simulate the most dangerous situation during the interaction between ice and structure, that is, the ice-induced vibrations of steady-state type. A simulation methodology to realize structural steady-state vibration is proposed; it can simulate a special phenomenon of negative damping. The calculation of effective ice pressure is accomplished by an empirical formula which considers the dependence of the crushing strength on the ice velocity. The most important contribution of the simulation method is to capture the steady-state vibration phenomenon. The presented simulation methodology is conducted on the same model test introduced in a referenced study to verify the efficacy. Calculational examples show good agreements with the results of the model test, and the frequency contents of the generations coincide well with the targets. They directly prove the validity of the proposed simulation method. In addition, the numerical simulation method can be used in connection with finite element programs to perform a steady-state vibration analysis of offshore structures.
In quasi-static tests of large-scale structural columns and/or columns under large axial loads, the lateral friction force between the column and the loading system can become a significant problem: they may cause considerable deviation between the measured lateral force and the actual reaction force of the column, especially under large axial compression load. Many researchers have come up with different methods to reduce or eliminate the influence of such friction force. In this article, previous treatments on the lateral friction force in quasi-static tests are first discussed. A shear force measurement device, for accurate measurement of the friction force, is then presented and calibrated. Based on the friction forces measured by the device in real tests, a simple model is proposed to predict the lateral friction force in quasi-static tests. Using the model, the measured lateral force in such tests can be corrected to obtain the actual reaction force of the column when a friction measurement device is absent. The proposed model and the correction method are then validated using results from several previous tests.