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Experimental and numerical studies were conducted to investigate interaction between reinforced‐concrete grid frame (CGF) and ceramsite foam concrete (CFC) infill. In the experiments, compressive tests were performed on the CGF and RC grid frame filled with the CFC which forms a composite wall, namely CGFW. To investigate the mechanical properties of the CGFW and the interactions between the CGF and CFC infill, the failure modes, integral stiffness, local strains, and load distribution coefficients of the composite wall were analyzed. The experimental results indicated that the CFC infill could uniformly transmit loads and significantly improve the bearing capacity and vertical stiffness of the CGFW while reducing the ductility of the composite wall. The load distribution coefficients of the CFC infill were stable at 0.51 ± 0.06 before peak load and damage evolutions in concrete columns were effectively alleviated due to obvious interactions between the CGF and CFC infill. To evaluate the interaction mechanisms of the two, numerical analysis was carried out by changing the sizes of central grid, opening rates, and reinforcement ratios of the composite walls. The finite element model with plastic damage constitutive of concrete was calibrated by comparing the experimental results. The numerical results indicated that the interaction between the CGF and CFC infill was insensitive to changes in grid sizes, and the interaction between the two was significantly different with the same reinforcement method of frame beams and columns. In addition, the CFC infill played an important role in the stability of CGF as the opening rate significantly affected the mechanical properties of the CGFW, and a stable path of load transfer was the key factor to ensure the interaction between the CGF and CFC infill. [ABSTRACT FROM AUTHOR]

Summary: A reinforced concrete vierendeel beam (RCVB) is an open‐web structure formed by connecting the top and bottom chords through block‐shaped shear keys. In this study, the static load test was applied to understand the failure state and reinforcement ratios relationship with bending capacity of RCVBs. The results reveal that numbers of horizontal cracks appeared in the chord‐key node area of the bending‐shear section. The deflection development of specimens experienced elastic, elastic–plastic, and plastic stages. The failure of the beam was controlled by the deflection and the ultimate load increased with the reinforcement ratio. A combined model for calculating the bending capacity of the top chords under eccentric compression and the bottom chords under axial tension is proposed. With the measured strains the loading coefficient of the beams are 1.15–1.20. According to the Chinese code, the continuous loading after the longitudinal reinforcement of the bottom chord yielding can make the top chord concrete reach the ultimate compressive strain, and the loading coefficient of the beams are 1.1–1.2. Therefore, the proposed model and formulas can effectively calculate the flexural bearing capacity of RCVBs. The finite element analysis results further indicate that the proposed calculation model and algorithm are appropriate. [ABSTRACT FROM AUTHOR]

In order to advance the understanding of fracture failure mechanisms in concrete, a series of three‐point bend tests of pre‐notched specimens were conducted to study the characteristics of the fracture process zone. Electronic speckle pattern interferometry (ESPI) was used to determine the location and size of the cracks. The experimental results have shown that crack in the pre‐notched concrete beams will initiate when the load increases to 40% of the peak load (Pmax) and expands unstably after reaching the peak load. When the load drops to about 25% Pmax in the load drop section, a complete fracture process zone (FPZ) was developed, and the corresponding crack tip opening displacement is about 7.1 times to the critical crack tip opening displacement. The analysis of surface strain of concrete specimen showed that microcracks will initiate when the surface tensile strain of concrete reaches about 2 × 10−4; when the surface tensile strain value of concrete reaches 4 × 10−2, the FPZ will move forward; the length of the FPZ of concrete essentially remains the same in the entire fracture process, which is about 71% of the ligament height. The analysis of experimental data also shows that the size of the FPZ is not significantly affected by the cubic compressive strength of concrete. In addition, the tension‐softening curves of the specimens were finally determined by using the incremental displacement collocation method, and it is concluded that the critical width of the FPZ is related to the cubic compressive strength of the concrete. [ABSTRACT FROM AUTHOR]

This study investigates the failure mechanisms and strength of plate-tube-connected circular steel arches. The upper and lower chord of the arch are joined by a series of uniformly distributed steel plates in a radial direction. The chord of the arch mainly bears bending moment, shear force and axial force. The connecting plates mainly resist bending moment, so its failure mechanisms and strength design are different from the traditional truss arch with diagonal tubes and web-opening arches. In this paper, the finite element (FE) software ABAQUS is used to study the in-plane failure mechanism and stability bearing capacity of planar plate-tube-connected circular steel arches, which is subjected to full-span uniform radial load (FSURL), full-span uniform vertical load (FSUVL) and half-span uniform vertical load (HSUVL). The elastic buckling load formula of two-hinged plate-tube-connected circular steel arches is proposed under FSURL.. Also, the limited condition of avoiding local buckling is also proposed under FSURL. The stability bearing capacity design formula of the arch under FSURL is proposed. Studies have shown that under FSURL, the arch will be subjected to global elastoplastic failure, and the upper chord will exhibit a full-section yield at the scope of 1/4 L span and the lower chord will exhibit a full-section yield at the scope of 3/4 L span. Under F(H)SUVL, the global failure mode may occur. The global failure stability bearing capacity design formulas of the arch under FSUVL and HSUVL are also proposed. The FE results are in good agreement with these formulas. Finally, the design suggestions of plate-tube-connected circular steel arches are proposed. [ABSTRACT FROM AUTHOR]

Constitutive relationship of cast-in-situ phosphogysum was researched at prismatic specimen under uniaxial compression test using self-loading device, and the elastic modulus and Poisson's ratio were determined. Totally 38 specimens were made and divided into nine groups for testing. Effective data of 33 specimens were collected. Experimental results show that; test specimens rapidly appear splitting failure when the strain is close to ultimate strain. The ratio of residual stress to peak stress approximately ranges from 0. 5 to 0. 8, while the ratio of ultimate strain to peak strain is roughly between 1.1 and 1.6. Retarders have enormous influence on peak stress. When its mixing proportion becomes close to 0.3%, the peak stress can adopt 8.6 MPa, and the ultimate strain is approximate 2.54 x 10-3. When its mixing proportion significantly exceeds 0.3%, the peak stress is 2.8 MPa, and the ultimate strain is 2.01x10-3. The ratio of residual stress to ultimate stress is 0.7, while ultimate strain is 1.45 times than peak strain. This paper presents the three-part constitutive equation of cast-in-situ phosphogysum which can reflect all the characteristics of compression test. The elastic modulus is higher when the strength of cast-in-situ phosphogysum is higher. The elastic modulus can take 5 300 MPa when the mixing proportion of retarders is close to 0.3%. When the retarder significantly exceeds 0.3%, the elastic modulus is approximate 2 000 MPa. And the Poisson's ratio is 0.19. [ABSTRACT FROM AUTHOR]