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Half-Grouted Sleeve Connection (HGSC) is extensively applied in the Prefabricated Concrete (PC) structures. The performance of the PC structures after fire has become an interesting research topic. However, the post-fire mechanical behaviors of the HGSC are still an issue that needs to be studied in depth. The experimental results of twelve HGSC specimens with concrete cover under static tension after 25 °C to 600 °C are presented in this paper. In the experiments, the post-fire HGSCs' failure mode is just rebar tension fracture, not bonding failure. The properties, such as strength, elongation, ductility, and elastic modulus were analyzed, and the failure mechanism, elongation and bonding slip, influence of concrete cover, bonding behaviour of HGSC after high temperature were discussed. It was found that some post-fire tensile properties of the HGSC were obviously affected by the peak temperature and the concrete cover.

Half grouted sleeve connection is widely used in joining rebars in precast concrete structures. However, its mechanical behaviors at elevated temperatures remain to be a topic with little research. This paper presents experimental results of 12 half grouted specimens and 12 single rebars under static tension at different temperatures. The tensile properties of half grouted sleeve connection were found to be directly affected by the temperature, and some characteristics are different from that of the rebar. The results showed that the half grout sleeves exhibited two types of failure, namely rebar fracture and rebar pullout due to bonding failure. The mechanical properties of specimens were similar to that of single rebars. When the temperature elevated, the failure mode and rebar breakpoint location may change. The bonding length that would be sufficient at room or low temperature, becomes insufficient at 600 °C. Suggestions about the bond length are given to avoid rebar pull out from the grout due to bond failure at elevated temperature.

In this paper, a mechanics based analytical truss model is proposed to predict the shear strength and deformation of conventionally reinforced coupling beams with span-to-height ratios less than 1.75 (referred to as short coupling beams). The model considers the yield of only parts of stirrups, and its load path is composed of a direct main strut connecting the compression zones at both ends of the beam and secondary struts balancing with stirrups. By satisfying the compatibility condition at the intersection node of the struts, the assignment of the applied shear load in the main and secondary struts, as well as the shear load-transverse displacement relationship of the beam, are determined. The shear strength predictions by the truss model are compared with test results of 37 conventional reinforced short coupling beams, which shows that it can accurately predict the shear strength with a coefficient of variation (COV) of 0.052, while the predictions provided by ACI 318-19 and GB 50010-2010 are relatively inaccurate (the COVs are 0.19 and 0.21, respectively). In addition, the skeleton curves of 27 short coupling beams are calculated by the truss model, and the results show that the predictions are in good agreement with the test results. In order to simplify the calculation, a simplified model is proposed based on the refined truss model. Although the accuracy of the simplified model is slightly reduced (the COV is 0.071), it is still significantly higher than those of the design codes. Based on the simplified model, a standardized design method, which indirectly considers the beam deformation capacity, is provided for practical shear design.

Pushover and nonlinear dynamic analysis method are applied to analyze the seismic performance of RC frame structure with or without slabs under the action of multiple factors in this thesis. Meanwhile, the structural response exerted by oblique seismic action is summarized from the theoretical formula derivation. By analyzing and comparing two kinds of established models, the results demonstrate that with various axial compression ratio and moment magnifying factors of columns, the seismic performance of the structure will be degraded when the influence of the floor is taken into account. And the increment of the values of axial compression ratio μ and moment magnifying factor of column η c with the floor exceeds that without the floor. Moreover, Earthquakes input along the principal axis can realize the “strong column weak beam” of the structure. Considering the influence of floor, when the value of axial compression ratio is higher than 0.56 or moment magnifying factors with the floor increases above 2.0, frame structure under oblique seismic action can form “strong column weak beam” yield mechanism.

Knowledge of the nonlinear elastic response and anharmonic properties of MgO single crystal is important for interpreting the seismically observed velocity variations in the Earth’s mantle and constructing reliable mineralogical modes of the Earth’s interior. However, investigations on these properties of it have not been performed sufficiently to date. So the nonlinear elastic response of the MgO is first studied by calculating the second-, third-, and fourth-order elastic constants. Results show that our predications on the high-order elastic constants exhibit excellent agreement with the available experimental ones and other theoretical values, which indicates that the present computational approach is suitable for the calculations of the high-order elastic constants and it can be expanded into other complex systems. Then on the basis of the elastic constants, the related anharmonic properties such as the first-order pressure derivatives of the second- and third-order elastic constants, Gruneisen constants of the long-wavelength acoustic modes, and ultrasonic nonlinear parameters are also investigated. The predications on the anharmonic properties first given in the present work are hoped to serve as a valuable guidance or reference for further related investigations.

An efficient method for reliability assessment of structural dynamic systems is proposed. In the proposed method, the reliability is evaluated by the equivalent extreme value distribution of structural dynamic systems, where an estimator-corrector scheme based on the principle of maximum entropy with fractional moments as constraints is adopted to derive such distribution. The fractional moments, which are of paramount importance to the efficiency and accuracy of reliability assessment, can be obtained by a multidimensional integral. To calculate such an integral, a new approach named unequal weighted quasi-Monte Carlo Simulation is put forward. In this approach, different strategies for the construction of unequal positive weights, the rearrangement of sampling points to be integration points and the determination of required number of points are explored. The integral for the evaluation of fractional moments is then determined efficiently based on the obtained integration points and the weights straightforwardly. Numerical example is studied to verify the proposed method. The investigations indicate that the proposed method is of accuracy and efficiency for reliability assessment of structural dynamic systems, with only a few hundreds of deterministic dynamic response analysis for a practical problem involving multiple random parameters.

Half grouted sleeve connection (HGSC) is widely used in joining rebars in precast concrete structures. Construction defects and fires are inevitable in practical projects. However, the mechanical behaviors of post-fire HGSC with construction defect remain to be a topic with little research. The present work presents experimental results of 66 post-fire HGSC specimens with construction defect under static tension at room temperatures. Results show that the tensile properties of post-fire HGSC are directly affected by the peak temperature and the construction defect, and some properties are different from that of the rebar. Post-fire HGSC exhibited two main types of failure mode: rebar fracture and bonding failure. The protruded rebar in some post-fire specimens obviously slides before the rebar fractured and the ultimate elongation becomes larger. Different type of construction defect has a different effect on the behavior of the specimens, and the effect depends on the weakening of the effective bond area between rebar and grout. The peak temperature and construction defect may make reliable HGSC be unreliable and not acceptable, once the corresponding peak temperature is near 600 °C. Results also show that the proposed method to simulate the construction defects of HGSC is feasible and the X-ray method is an effective way to detect the defects in HGSC.

The performance of the prefabricated concrete (PC) structures at elevated temperature becomes an important focus, once a fire occurs. The failure in fire of fully-grouted sleeve connection (FGSC) that extensively used in PC members will cause serious consequences. To fill this knowledge gap, the present work presents the experimental results of 15 FGSC specimens and 15 single rebar (SR) specimens by static tension. The results show that the mechanical behavior of FGSC specimens at high temperature is affected by the temperature and similar to that of SR. Two types of failure modes appear in the FGSC specimens, namely, rebar tension fracture and bond failure. The bond failure was observed at 600 °C. Based on the test results, the tension constitutive relation curves was established, and the bond strength design of FGSC at elevated temperatures were put forward to avoid the bond failure. A new prediction method for calculating mechanical property of prefabricated rebar connection at elevated temperature is proposed.

In reinforced concrete (RC) column footings, the soil stiffness can significantly affects the punching shear strength of the foundation slab. The present study conducted eccentric compression tests on three RC column footings considering the complex interaction between the soil and structure, and investigated the load-carrying capacity, displacement distribution, reaction distribution, failure mode, crack development, and strain distribution. The test parameter was flexural reinforcement ratio in the foundation slab. The test results showed that the footing specimen with lower reinforcement ratio was susceptible to brittle punching shear failure, and the flexural reinforcement ratio affected the crack distribution and the spalling of concrete cover. Since only one specimen was used in each flexural reinforcement ratio, however, the test results should be carefully considered. On the basis of the test results including existing studies, the effect of design parameters on the punching shear strength was evaluated. As a result, a new method was developed to predict the punching shear strength by addressing the eccentric compression force.

Half-grouted sleeve connections (HGSCs), which are extensively used in prefabricated concrete (PC) structures, have attracted considerable research interest, including their mechanical properties under fire. However, research on the post-fire behaviors of this type of connection under different cooling methods and paths is limited. To fill this knowledge gap, the present work presents the experimental results of 33 HGSC specimens subjected to various peak temperatures and different cooling methods. Results show post-fire tensile properties are significantly affected by the exposed peak temperature and subsequent cooling method. Two types of failure modes are observed on the basis of the exposed peak temperature and cooling method, namely, rebar tension fracture and bond failure. The bond length of HGSC designed for room temperature is sufficient after a fire if the connection is naturally or air-cooled after peak temperature; whereas the bond length must be increased if water cooling is applied. Finally, a set of stress–strain relationships of HGSC and rebar is suggested for the post-fire performance evaluation and numerical simulation of PC structures with HGSCs.

Concrete filled tubular (CFT) columns are being more and more utilized in construction of tall buildings and bridges. Xiao recently developed a new CFT column system, named as confined concrete filled tubes (CCFT), and validated its excellent load carrying capacity and ductility, by static and simulated seismic loading tests. This paper reports the impact behavior of CFT and CCFT stub columns. The impact responses of concrete filled steel tubes (CFT) and the confined concrete filled steel tubes (CCFT) were investigated using a high-speed gas gun. Experimental parameters included the confinement details and impact speed. Dynamic strains and the failure patterns are discussed. The test results demonstrate the effectiveness of lateral confinement to improve the dynamic impact behavior of CFT columns. Comparisons were also made between the test results and the analytical results using LS-DYNA. The trend of the stress wave propagation in the CFT specimen was reasonably well predicted.

Since knowledge of the structure and elastic properties of Ta at high pressures is critical for addressing the recent controversies regarding the high-pressure stable phase and elastic properties, we perform a systematical study on the high-pressure structure and elastic properties of the cubic Ta by using the first-principles method. Results show that the initial body-centered cubic phase of Ta remains stable even up to 500 GPa and the high-pressure elastic properties are excellently consistent with the available experimental results. Besides, the high-pressure sound velocities of the single- and poly-crystals Ta are also calculated based on the elastic constants, and the predications exhibit good agreement with the existing experimental data.