Advances in Structural Engineering

In this paper, a novel arch-shaped BFRP tube with longitudinal BFRP bars pre-bonded on the inner wall is proposed and fabricated. It can provide strength in both circumferential and longitudinal directions and is suitable for the rapid construction of arch bridges in island environments by filling with seawater sea-sand coral aggregate concrete (SWCC) in situ. Ten SWCC-filled BFRP tubular arches were fabricated and tested under monotonic loading. Test variables include the wall thickness of the BFRP tube, the radius angles of the arch, and with or without pre-bonded BFRP bars. Test results showed that the failure modes of arches without BFRP bars were bending failure under the loading point. The ultimate bearing capacities were increased by 33.1% and 71.7% as the wall thickness increased from 2 mm to 3 mm and 4 mm, respectively. The failure modes of arches containing pre-bonded BFRP bars were bending-shear failure close to the loading plate. The ultimate bearing capacity of arches, which containing BFRP bars, with a wall thickness of 2 mm, 3 mm, and 4 mm increased by 215%, 248%, and 189%, respectively, compared with the specimens without BFRP bars. The integrity and ultimate bearing capacities of arches decreased with the increase of the radius angle and their failure modes exhibited obvious brittle damage characteristics. The proposed new type of arch has good prospects for application in the marine environment.

The concrete deck of steel-concrete composite bridges made via prefabricated construction consists of precast slabs and construction joints between the slabs. When the age difference between the longitudinal joint concrete and precast slab concrete (new-old concrete) across a beam section is considered, the time-dependent characteristic of the assembled deck is different from that of the whole prefabricated deck. Based on the virtual work principle, differential equations were established to analyse the influence of the time-dependent characteristics of new-old concrete across a beam section on the shear lag effect of the composite beams. The analysis of examples showed that the proposed model was more accurate than the traditional model, which ignores the concrete age difference across a beam section, especially when analysing the long-term stress of joint concrete. The long-term stress of the joint concrete obtained by the proposed model decreased faster than that obtained by the traditional model with time, which increased the non-uniformity of the distribution of stress along the concrete flange. Overall, the proposed model could reasonably forecast the long-term performance of composite beams with assembled decks, which is beneficial to the life-cycle design and service behaviour analysis of composite bridges.

The old existing reinforced concrete (RC) structures in Taiwan are susceptible to severe damage under earthquakes because of the soft-story mechanism. Moreover, the effects of near-fault ground motions often contain a long period of velocity pulse and permanent ground displacement. This study is based on the tri-axial shaking table test conducted at the National Center for Research on Earthquake Engineering in Taiwan and a series of seismic performance evaluations of a non-ductile RC structure in Taiwan. Finite element analysis (FEA) will be conducted to simulate the linear and nonlinear behavior of the seven-story building. This accommodates the damage plasticity model for concrete and the elastic-perfectly plastic model for reinforcement. Comparison of the results between the experimental test and numerical model showed that the similarity of the vibration period has a great influence on the simulation results. The findings showed that the data of acceleration and displacement behavior corresponded with the experimental results in a satisfactory margin. Also, the damage mode is very similar to the shaking table test results. The study found that using FEA can satisfactorily simulate the seismic performance of mid-rise buildings under a near-fault earthquake.

Over the past few decades, ultra-high performance concrete (UHPC) has been widely studied and applied because of its outstanding mechanical properties. A large number of studies have been conducted on the uniaxial static and dynamic performance of UHPC materials, however, limited investigations exist on the triaxial compression properties of UHPC. In this study, 98 cylindrical samples of UHPC with different steel fiber volumetric ratios (0.0%–1.5%) were tested to investigate the triaxial behavior of UHPC under different confining pressures (0 MPa–40 MPa). The confining pressure and steel fiber contents have clear impact on the triaxial strength, failure mode, crack width, and the angle between the oblique crack and the axial direction. The triaxial compressive strength and compressive toughness of UHPC subjected to various confining pressures are obtained from the tests and discussed in the study. Based on the testing data, the triaxial compression failure criterion of UHPC is established according to the unified strength theory. Finally, the simplified empirical equations for the full stress-strain curves of UHPC specimens subjected to uniaxial and multiaxial loads are derived, and good agreement with the experimental results is achieved.

Due to the excellent cracking prevention behavior of ultra-high toughness cementitious composite (UHTCC), the stud number and reinforcement ratio of composite bridge decks could be reduced, and hence the fatigue properties could be improved. In this study, a theoretical model was proposed to predict ultimate flexural capacity of steel-UHTCC composite bridge decks with different shear connection degrees. To evaluate the accuracy of the theoretical model, 10 examples were designed for finite element (FE) validation and parametric study, and the results indicated that the theoretical model can predict the ultimate flexural capacity of steel-UHTCC composite bridge decks with satisfactory accuracy. Then, quantitative analysis was conducted to reveal the effect of key design parameters on the ultimate flexural capacity. The design parameters involved in the parametric study included: (1) normalized stud number; (2) shear span length; (3) thickness of UHTCC slab; (4) reinforcement ratio; and (5) the number of longitudinal plate ribs. The reasonable range of the normalized stud number in a shear span can be determined between 0.5 and 1 in practical design and increasing of longitudinal reinforcement ratio has limited effect on ultimate flexural capacity of steel-UHTCC composite bridge decks.

A reasonable prediction for the peak strength of reinforced concrete (RC) columns is paramount for the seismic performance evaluation of RC structures. The available prediction models are commonly dependent on the failure mode, and each of them is only applicable to the columns with a particular one. However, the failure mode of RC columns is difficult to be identified accurately in prior, leading to the inconvenience of predicting its peak strength. To overcome this shortcoming, a probabilistic approach was proposed using Bayesian neural network (BNN) to develop a failure-mode–independent model for predicting the peak strength of RC columns directly. The results indicated that the developed model produces reasonable prediction for the peak strength of RC columns failing in different modes. For the training subset, the mean prediction accuracy of the flexure-dominated, flexure-shear-dominated, and shear-dominated columns is 0.997, 0.997, and 0.998, respectively. For the testing subset, the corresponding mean prediction accuracy is 0.957, 0.952, and 0.943. Compared to existing probabilistic models, the developed model exhibits better performance in reducing the uncertainties in peak strength prediction. Compared to existing deterministic models, the developed model could predict the peak strength of RC columns in terms of the confidence interval. In particular, if the confidence interval of peak strength is defined as the mean plus and minus two times standard deviation, 98.9% and 98.4% of the training subset and testing subset are covered. Therefore, the developed model is beneficial for engineers to address the confusion, namely, which peak prediction is the most probable one, when several deterministic models exist for a specific specimen.

In order to study the seismic performance of the reinforced concrete staggered slab-column structure, one 1/7 scaled test specimen was fabricated and tested. The acceleration response, displacement distribution, dynamic characteristics, torsion responses, failure mechanism, shear force, and strain of test specimen were measured and evaluated. Test results indicated that the natural frequency and acceleration magnification factor of the test specimen gradually reduced, while the floor shear force and torsion response gradually increased. Meanwhile, the maximum inter-story drift angle of test specimen in the elastic and elastic-plastic stage was 1/196 and 1/78, respectively, indicating that the lateral stiffness of staggered slab-column structure was relatively small. The inter-story angles of the second and fifth floors were larger than adjacent floors. It was suggested that the stiffness of the test specimen was inhomogeneously distributed due to staggered slabs and a lack of frame beams. The damage of columns between staggered slabs was obviously larger than other columns. The plastic hinges were successively observed at slab-column junctions on the first and second floor and bottom of columns. Finally, the plastic hinges at slab-column junctions lost their capacity, followed by plastic hinges at the bottom of columns, and the test specimen collapsed. The failure process of the staggered slab-column structure exhibited undesirable brittle failure mode. Based on the experimental results, several design suggestions were proposed to improve the overall seismic behavior of the staggered slab-column structure. Such comprehensive research helps enhance understanding of this newly developed type of structure.

The sparse regularization (SReg) model is widely used for structural damage identification by employing the sparsity peculiarity of the structural damage. The conventional SReg model often separately conducts damage identification on each measurement, while ignores the utilization of the similarity information among different measurements. In this paper, we propose a novel joint sparse regularization model for structural damage identification. In detail, combined with the sparsity of the structural damage by the conventional SReg model, our model employs the similarity of different measurements to further improve the damage identification performance, which is realized by the generalized fused lasso penalty. Numerical simulations on the six-bay planar truss structure and experimental studies on the cantilever beam structure illustrate that the damage identification accuracy of our model is promoted 3.59% and 20.75% than the conventional SReg one, respectively.

The seismic performance analysis of steel–concrete composite frames involves, as known, the interaction of several load-bearing components that should be properly designed, with multiple geometrical and mechanical parameters to account. Practical recommendations are given by the Eurocode 8 (EC8) – Annex C for the optimal detailing of transverse rebars, so as to ensure the activation of conventional resisting mechanisms. In this paper, the attention is focused on the analysis of effects and benefits due to a novel confinement solution for the reinforced concrete (RC) slab. The intervention is based on the use of diagonal steel spirals, that are expected to enforce the overall compressive response of the RC slab, thanks to the activation of an optimized strut-and-tie resisting mechanism. The final expectation is to first increase the resistance capacity of the slab that can thus transfer higher compressive actions under seismic loads. Further, as shown, the same resisting mechanism can be beneficial for the yielding of steel rebars, depending on the final detailing of components, and thus possibly improve the ductility of the system. To this aim, a refined finite element (FE) numerical analysis is carried out for several configurations of technical interest. The in-plane compressive behaviour and the activation of resisting mechanisms are explored for several spiral-confined slabs, based on various arrangements. Major advantage is taken from literature experimental data on RC slabs that are further investigated by introducing the examined confinement technique. The attention is hence given to the local and the global structural effects due to different arrangements for the proposed steel spirals. As shown, once the spirals are optimally placed into the slab, the strength and ductility parameters of the concrete struts can be efficiently improved, with marked benefits for the overall resisting mechanisms of the slab, and thus for the steel–composite frames as a whole.

Simulating the stochastic traffic load has been an important issue for bridge condition evaluation. This paper proposes an improved cellular automaton for stochastic traffic load simulation with consideration of axle load and microscopic interaction. The cells, neighbors, transition rules and boundary conditions in the improved model are all redefined. The cell length can be manually defined with any value. The vehicle load can be precisely simulated using axle load if the cell length is set small or using concentrated load when a large cell length is defined. Acceleration based transition rules are proposed, and different acceleration for each vehicle can be computed to more reasonably simulate the microscopic behavior. The feasibility of the proposed model is validated through comparisons on traffic flow simulation and load effect quantification with in-field weigh in motion data and other models. The results indicate that the proposed model improves the existing models both in vehicle load simulation and traffic flow simulation and can be used for stochastic traffic load simulation for bridges with any length.

Flow separation and reattachment over bluff bodies has been a primary concern in wind engineering community as it may generate large suction pressure. This study re-visits the characteristics of wind pressure underneath the separated shear layer, with emphasis on diagnosing the underlying dynamic properties. Nonlinear dynamic analysis techniques, namely recurrence plot and recurrence quantification analysis are applied to reveal and compare the wind pressure dynamics associated with different test conditions. The results indicate that the dynamic behaviour of wind pressure is closely tied with leading edge shape, turbulence intensity, as well as turbulence scale. Generally, the underlying dynamics of wind pressure become less deterministic as the measurement position moves from leading edge towards downstream. Such pattern is reversed once the descriptive indicator reaches its minimum. The position of such minimum value corresponds well to the downstream boundary of the reverse flow region. Moreover, the minimum value of dynamic descriptive indicator, as well as the reverse position in its distribution pattern, is correlated with the leading edge shape. On the other hand, the minimum value of dynamic descriptive indicator is also dependent on turbulence scale, while the reverse position in the distribution pattern of dynamic descriptive factor is dependent on turbulence intensity.

Precast shear wall is an important structural form of building industrialization and housing industrialization. In order to improve the seismic performance of precast shear wall, the reinforced tenon is presented to improve the shear performance of precast shear wall joints. In order to grasp the further difference of mechanical properties of reinforced tenon precast shear wall under different axial compression ratios, the low cyclic reversed loading tests were carried out on a cast-in-situ shear wall specimen and two reinforced tenon precast shear wall specimens with different axial compression ratios respectively. According to the test results, the hysteresis characteristics, bearing capacity, steel strain, energy dissipation capacity, rigidity degeneration and other seismic performance parameters of the three specimens were analyzed. The test results show that the failure modes of the three specimens were same, which was compression-bending failure. Connection form of reinforced tenon has good shear resistance. The reinforced tenon precast shear wall with the larger axial compression ratio has the worse ductility, the higher bearing capacity and stronger the rigidity.

Application of basalt fibre reinforced polymer (BFRP) bar reinforced seawater sea-sand concrete structures in marine and coastal buildings could bring both environmental and economic benefits. As BFRP bar reinforced seawater sea-sand concrete members are likely to be exposed to temperature variations during their service life, the bond durability between BFRP bar and seawater sea-sand concrete should be well understood. This paper investigated the effects of thermal cycling, such as target temperature (i.e. amplitude of variation) and cycling times, bar diameter and concrete strength on the bonding behavior of BFRP bars in seawater sea-sand concrete by pullout test. It is found that target temperature and cycling times lead to a significant reduction of BFRP bar-to-seawater sea-sand concrete bonding, which is mainly attributed by the degradation of BFRP under thermal cycles. Through the method of scanning electron microscopy, microstructure of BFRP is examined and the bond mechanism considering the effect of temperature variations is clarified. Finally, theoretical model is proposed to predict the bond stress-slip relationship of BFRP bars in seawater sea-sand concrete. Accuracy of the predictions is validated by the experimental results.