To investigate the shear performance of Italian poplar laminated veneer lumber(LVL)beams with opening in the bending-shear region,six standard specimens were designed and tested under four-point bending.The shear failure mechanisms of the LVL beams with opening under various parameters were analyzed.Using the extended finite element method and ABAQUS software,a finite element model of perforated beam with virtual cracks was developed.Parametric analyses were performed considering variations in the diameter-to-height ratio,opening shape,and opening center eccentricity,using the validated model.The results show that the unperforated beam experiences bending failure due to tensile cracking at the mid-span.In contrast,beams with circular opening experience longitudinal shear failure at the ends due to stress concentration around the opening perimeter.The maximum transverse tensile strain around the opening perimeter forms an angle of approximately 45°or 225°relative to the longitudinal axis of beam,consistent with the crack initiation angle.As the diameter-to-height ratio increases to 0.5,both cracking and ultimate load capacities of the beams with circular opening significantly decrease,exhibiting more brittle shear failure.When the diameter-to-height ratio increases from 0.3 to 0.4 and 0.5,the ratio of cracking to ultimate load capacity increases from 0.79 to 0.80 and 0.81,respectively.Using carbon fiber reinforced polymer(CFRP)wrapping around the openings effectively suppresses crack propagation and enhance the structural performance of the perforated beams.For the beam with a diameter-to-height ratio of 0.4,the ultimate load decreases by 17.9％and 5.22％,respectively,for one and two layers of CFRP wrapping,compared to the unperforated beam.When comparing circular-opening beam(diameter-to-height ratio of 0.3)to those with square-opening of the same diameter,the square-opening beam shows a 19.35％and 7.81％reduction in cracking and ultimate load capacity,respectively.Increasing the opening center eccentricity is found to improve both cracking and ultimate load capacities.The prediction formulas for the cracking and ultimate load capacities of LVL beams with opening were proposed.The prediction for cracking load is relatively conservative,and the average error between the predicted and experimental results for the ultimate load is 8％.
Carbon fiber-reinforced polymer-steel composite bars (C-FSCBs) and coral sea-sand aggregate seawater concrete (CSSC) are attractive choices as construction materials for island and atoll engineering construction. Understanding the bond behavior between the C-FSCB and CSSC is crucial for evaluating the mechanical properties of C-FSCB-reinforced CSSC structures. In this study, the bond-slip behavior between the C-FSCB and CSSC was experimentally assessed via pullout tests. The influence of various factors on the bond behavior was discussed, and the bond mechanism between the C-FSCB and CSSC was analyzed. The results indicate that, unlike steel bars, the low rigidity of fiber-reinforced polymer caused surface fiber stripping (i.e., shear damage) of the C-FSCB after interface slip, consequently reducing the squeezing fragmentation of concrete between the ribs. As the diameter and bond length of the C-FSCB increased, the bond strength decreased. Compared to specimens with C-FSCBs, the bond strength of specimens with steel bars of the same diameter increased by 17.9%. The degree of coarse aggregate fracture at the CSSC interface in the splitting failure was much higher than that of normal concrete. Based on existing research data, a formula for calculating the bond strength of C-FSCBs in CSSC has been established to determine the anchorage length of C-FSCBs, and the calculated values accurately predicted the test values.
Combining the advantages of partially encased composite structure (PEC) and corrugated steel web, a new type of composite PEC beam with corrugated web was proposed in this paper, namely corrugated webbed PEC (CWPEC) beam. In order to investigate the structural performance of the proposed CWPEC beams, four specimens were designed and fabricated. Four-point bending tests were carried out to study their flexural performance and failure modes. The failure process, load-displacement curve and strain distribution of the tested specimens were analyzed. Experimental results showed the high load carrying capacity and superior ductility of the proposed concept. Parametric study indicated that the concrete strength was increased from C30 to C50, the ultimate load slightly increased by 3.38%. The flange strength decreased from Q355 B to Q235, the ultimate load reduced by 9.17%. The flange width decreased from 250 mm to 200 mm, the ultimate load decreased by 22.21%. As comparison, the increase of steel flange width is more efficient to improve section moment capacity. Further analysis verified that the flexural strength of CWPEC beam was mostly provided by flanges with little contribution from the corrugated web. Finally, based on the quasi-plane assumption, prediction formulas for cracking moment and ultimate moment of CWPEC beams were proposed.
A suitable constitutive model for describing the damage behavior of ultra-high performance concrete (UHPC) under various loading histories plays a vital role in analyzing its structural performance. In this work, a consistent elastoplastic damage model is developed for UHPC containing coarse aggregate (UHPC-CA) subjected to static and fatigue loads, in which the driving and alleviating effects induced by the inclusions of coarse aggregate and steel fiber are considered. For damage evolution, based on the acting mechanism of the non-uniformity of stress wave propagation determined by the loading rate on the mechanical responses of UHPC-CA, the loading rate is skillfully integrated into the damage evolution rule to achieve the consistent description of mechanical behaviors of UHPC-CA under static and fatigue loading conditions. Regarding plasticity growth, an empirical plastic deformation model is adopted to improve the computational efficiency of structural nonlinear analysis. To verify the applicability of the proposed model, a user-defined UMAT subroutine is further developed for the subsequent numerical implementation. The comprehensive comparisons between the numerical predictions and independent experimental results at both the material level and structural level solidly demonstrate the capacity of the consistent model to capture the main features concerning the mechanical performance of UHPC-CA subjected to different loading paths.
Irregular buildings that occupy a certain proportion on regional scales are prone to suffer serious damage from earthquakes due to the influence of lateral-torsional coupling effect. However, the current regional seismic damage simulation methods are mainly based on two-dimensional simplified models, which cannot take into account the spatial characteristics of irregular buildings. In addition, the refined finite-element method is unsuitable for the simulation of a host of buildings on a regional scale. This paper proposes a moderately refined seismic damage simulation method for building groups with high efficiency to consider the spatial irregularity characteristics of structures. The moderately refined layer element model is established to simulate the nonlinear behavior of each story of the building with irregular plan configurations. For the elevation-irregular structures, the proposed model can also be used by properly combining the elements representing various stories in series. Additionally, a simplified approach of considering P-∆ effect is incorporated by adding equivalent lateral forces to nodes and the method for determining the hysteretic parameter and backbone curve parameters of the proposed model is illustrated. Then, a two-level accelerated dynamic analysis method is proposed to reduce computation time for seismic damage simulation in region, which involves a perturbation nonlinear dynamic governing equation for a single structure and an OpenMP parallel solution strategy for structure groups. Finally, the two individual numerical examples and the seismic damage simulation for a region are performed to demonstrate the validity and efficiency of the proposed method.
