To investigate the dynamic compressive properties of concrete after high temperature and rapid cooling, an experimental study was carried out by considering five temperatures and four strain rates. The coupling effect of high temperature and strain rate on concrete damage morphology and mechanical parameters was comparatively analyzed. The main conclusions are as follows: the compressive damage morphology of concrete is affected by strain rate development trends of significant variability under different temperature conditions. As the strain rate increases, the compressive stress and elastic modulus of concrete are gradually increased. As the temperature increases, the increase in compressive stress is gradually reduced by the strain rate. For the temperatures of 20 °C and 800 °C, the increase in compressive stress by the strain rate is 38.69% and 7.78%, respectively. Meanwhile, SEM and CT scanning technology were applied to examine the mechanism of the effect of high temperature and strain rate on the mechanical properties of concrete from the microscopic perspective, and the corresponding constitutive model was proposed.

Recycled concrete, which is formed by replacing coarse aggregates in ordinary concrete with recycled aggregates (RA), is of great significance for the secondary utilization of waste building resources. In civil engineering, concrete structures are sometimes subjected to a compression–shear multiaxial stress state. Therefore, research on the compression–shear multiaxial mechanical properties of recycled concrete plays an important role in engineering practice. To explore the effect of RA replacement rate on the compression–shear properties of recycled concrete, an experimental study was carried out using a compression–shear testing machine and considering five RA replacement rates and five axial compression ratios. Consequently, the failure modes and mechanical property parameters under different working conditions were obtained and were used to analyze the effects of RA replacement rate and axial compression ratio on the shear stress of recycled concrete. Eventually, the following conclusions were reached: With the growth of axial compression ratio, the shear cracks exhibit a developing trend along the oblique direction, and the friction traces on the shear surface are gradually deepened. As the replacement rate increases, the number of shear cracks is gradually increased, accompanied by increasing broken fragments falling off from the shear interface. Since the action of the axial compression ratio can effectively improve the mechanical bite force and friction on the shear interface of recycled concrete, as the axial compression ratio increases, the shear stress is gradually increased. On the other hand, due to the initial damage of RA and its weak adhesion with cement mortar, the shear stress is gradually reduced with the increase of RA replacement rate. Meanwhile, the increase in shear stress shows a gradually decreasing trend with the growth of axial compression ratio. Specifically, for the RA replacement rates of 0% and 100%, the shear stress increased by 4.06 times and 3.21 times, respectively, under the influence of the axial compression ratio. Under different axial compression ratios, the shear stress was reduced by 43~46%, due to the increase of RA replacement rate. In addition, based on the octahedral stress space and the principal stress space, a compression–shear multiaxial failure criterion and shear stress calculation model for recycled concrete were proposed, by considering the effect of the RA replacement rate. The outcomes of this research are of great significance for engineering applications and the development of recycled concrete.

The bending stiffness of cables is an important influencing parameter in the analysis of cable structures, and the modeling of cables with bending stiffness has always been a key concern. This paper proposes an accurate beam formulation for planar cables with bending stiffness, in which the deformation–strain relationship is accurately described, thus enabling the geometrically exact form finding of planar cables. After the kinematics of the cable geometry are described, the strong- and weak-form equilibrium equations of the cable are derived, and then the finite element implementations are presented. Three typical examples of cable structures are also presented; the numerical results demonstrate that the presented beam formulation shows stable and accurate numerical performance. The proposed formulation achieves rapid convergence when the number of elements reaches 20. The analysis of a suspension bridge shows that considering bending stiffness has little influence on the completed bridge state, with the error between the calculated hanger forces and the design values remaining within 1.5%. However, in the free cable state, considering bending stiffness causes a saddle pre-offset variation of approximately 5 cm, while the sag difference reaches approximately 1 m. The results demonstrate that the proposed formulation is of significant importance for planar cable form finding problems.

This paper presents a new plane stress model for the dynamic analysis of multilayer composite beams with interlayer slip effects. In this model, the cross section of a multilayer composite beam is transformed into an equivalent plane stress cross section. Based on the equilibrium, constitutive and geometric equations of the plane stress problem, state equations are derived in terms of a set of state variables. The state variables are then expanded in Fourier series, and the state equations are solved using the state-space method. The proposed computational model makes it convenient to account for slip at each interface and can represent the entire transition of an interface from fully slipped to fully bonded. Interlayer slip and the corresponding interaction forces are incorporated naturally into the derivation of the governing equations, and the model gives accurate results. A steel–concrete–steel composite beam, a four-layer composite beam and a laminated timber beam are analyzed as examples of multilayer composite beams under both static and dynamic loading. The static analysis results are in good agreement with the literature results, with a maximum error of 0.63% for the maximum mid-span deflection and only 0.143% for the maximum interlayer slip value. Compared with finite element results, the natural frequencies and buckling loads obtained from the dynamic analysis exhibit maximum relative errors of 2.87% and 3.77%, respectively. The relationship between axial force and natural frequency is also presented, which verifies the accuracy and reliability of the proposed model and calculation method.

Steel–concrete composite beams are widely used in building and bridge engineering; however, the impact response of Steel–Coarse Aggregate–Ultra-High Performance Concrete (Steel–CA–UHPC) composite beams remains insufficiently quantified, and no beam-specific dynamic capacity formula is available. To address this gap, companion static testing and drop-weight impact tests were performed on full-scale simply supported steel–CA–UHPC composite beams under single and repeated impacts, followed by development of a strain-rate-dependent dynamic increase factor (DIF) model and a capacity prediction framework. The companion static specimen reached 448 kN, whereas the 5 m impact cases produced peak forces of 930.0–940.4 kN, corresponding to 2.08–2.10 times the static level, with the initial peak forming within 1.0–1.1 ms. Dynamic failure was marked by rapid mid-span cracking of the CA–UHPC slab and brittle shear fracture of studs, while repeated impacts mainly accelerated cumulative damage before the final high-energy strike. Static–dynamic displacement comparison further revealed much more abrupt deformation concentration under impact loading. A revised static capacity formula reduced the prediction error from 4.46% for the code-based method and 1.00% for the literature model to 0.74%. Combined with the fitted DIF–strain-rate relation, the proposed framework reproduced the measured dynamic capacities with errors of −4.63% to 9.75%. The study provides member-level evidence and a practical DIF-based method for evaluating the impact resistance of steel–CA–UHPC composite beams.