In this article, frequency analysis of multi-sized hybrid nano-composites (MHC) disk (MHCD) resting on elastic media and located in an environment with gradually changed temperature feature is presented. Carbon fibers (CF) or carbon nanotubes (CNTs) in the macro or nano sizes respectively are responsible for reinforcing the matrix. For prediction of the efficiency of the properties MHCD’s modified Halpin-Tsai theory has been presented. The strain-displacement relation in multi-sized laminated disk’s dynamics through applying third-order-shear-deformation-theory is determined. The energy methods called Hamilton’s principle is applied for deriving the motion equations along with boundary conditions, which has ultimately been solved using generalized differential quadrature method. The deflection as the function of time can be solved by the fourth-order Runge-Kutta numerical method. At the final stage, the outcomes illustrate that patterns of FG, fibers’ various directions, the W _CNT and V_F factors, top surface’s applied temperature have considerable impact on the MHCD’s dynamics. Another important consequence is that MHC structure with FG-A and UD patterns have a similar effect on the dimensionless natural frequency of the GPLRC disk, while FG-X has the lowest stability and natural frequency. A useful suggestion is that increasing the value of the length to thickness ratio of MHC not only decreases the central deflection of the structure through time but also causes to decrease real-time domain changes for the MHC viscoelastic annular plate. Numerical results declare that viscoelastic disks fabricated from the hybrid nanocomposites can endure higher frequencies compared with those consisted of conventional composites.

Modular steel construction (MSC) consists of the off-site prefabrication of a fully finished module and the on-site assembling of the module unit. The popularity of MSC is on the rise, attributable to its technical advantages of speed and quality of buildings with repetitive units. Inter-module connection is critical for the overall stability and load-bearing capacity of MSC. An innovative, fully prefabricated liftable connection (FPLC) using standard corner fittings and long stay bolts is proposed in this paper. This paper focuses on the axial compressive behavior and design of FPLC. Five full-scale specimens were tested under axial compression. Local buckling of the column and shear of the long stay bolts were observed during the test. It can be concluded from the test results that the load-bearing capacity may decrease as the number and diameter of the stay bolts increase. A three-dimensional nonlinear finite element model (FEM) was developed and validated against the test results by general purpose finite element software ABAQUS. Furthermore, a parametric study was conducted using the verified FEM to provide a better understanding of the axial compressive behavior of the FPLC. The results of the parametric study indicated that the corner fitting can be up to 15% lighter for columns with thicknesses of 6 mm and 8 mm without substantial reduction of the axial load-bearing capacity of the FPLC. Moreover, the location of the column can be adjusted to achieve a uniform Von Mises stress and equivalent plastic strain (PEEQ) distribution of the connection. The presented research work provides an engineering-practical inter-module connection on its axial compressive behavior, which will provide helpful references for further application of MSC.

As a common building insulation material, foamed concrete has been widely used in engineering practice. However, the contradiction between compressive strength and thermal conductivity has become the main problem limiting the development and application of foamed concrete. Therefore, high-performance foam concrete (HPFC) with high compressive strength and low thermal conductivity was prepared by using graphene oxide (GO), fly ash, and polypropylene (PP) fiber as the main admixtures, and taking compressive strength, thermal conductivity, and microstructure as the main indices. Scanning electron microscopy, X-ray diffraction (XRD), and thermogravimetry–differential scanning calorimetry (TG-DSC) were employed to examine the mechanisms of HPFC. The results showed that when the content of fly ash was 25–35 wt%, PP fiber was 0.2–0.4 wt%, and GO was 0.02–0.03 wt%, the FC’s compressive strength increased by up to 38%, and its thermal conductivity reduced by up to 3.4%. Fly ash improved the FC’s performance mainly through filling, pozzolanic activity, and slurry fluidity. PP fiber enhanced the performance of FC mainly through bridging cracks and skeletal effects. The addition of GO had no significant impact on the type, quantity, or hydration reaction rate of the hydration products in these cement-based materials, and mainly improved the FC’s microstructural compactness through template action and crack resistance, thereby improving its performance.

Special-shaped concrete-filled steel tube (SS-CFST) columns can be embedded in the wall, thus preventing the columns from protruding. This feature makes it popular in steel residential buildings. This paper proposes a new special-shaped concrete-filled square steel tube (SS-CFSST) composite column composed of multiple square steel tubes connected by steel hoops to form L-, T- or cross-shaped sections. Eight specimens were tested under axial loads with section shape, construction method, slenderness ratio, steel tube thickness, and steel strength as variation parameters. The structural performance, such as failure modes, peak load, load–displacement curves, load–strain curves, and Poisson’s ratio of the steel tubes, were analyzed. The tests illustrated that the failure modes of hoop-type specimens and weld-type stub columns were mainly the local buckling of steel tubes and bending failure, and those of the weld-type slender columns were mainly overall bending failure. The load-carrying capacity of the hoop-type specimen was higher than that of the weld-type specimen with the same cross-sectional dimensions and slenderness ratio. Next, the stress–strain relationship model of core concrete in the SS-CFSST composite column was established by considering the restraint effect of the connection coincidence area of steel tubes and steel hoops on concrete. Additionally, the finite element model (FEM) of the column was established using this constitutive model. By comparing the failure modes, load–strain curves and bearing capacities obtained from the tests and FEM, the established FEM can accurately evaluate the mechanical properties of SS-CFSST composite columns with steel hoops under axial compression.

The presence of residual stress in steel members can significantly compromise the stiffness and fatigue life of steel structural components. This influence becomes more serious for the wide butt welds in the construction of large-sized steel members due to the different residual stress distribution from the normal size butt welds. This paper experimentally studied the residual stress in the wide butt welds through an 8-experiment test program. High residual stress was produced during the wide butt welding and this stress was observed to be even higher than the yield strength of the steel. Moreover, this residual stress in the steel plate was firstly compressive and then transferred into tensile stress with the increase in the distance away from the butt weld line. The magnitude of the residual stress increased with the increase in the width of the welding seams. This paper also developed a finite element model by SYSWELD to simulate the residual stress produced by the wide butt welding. The accuracy of the FE simulation was checked by the reported test results. In order to reduce the residual stress, the ultrasonic peening method was adopted. The analysis results indicated that ultrasonic peening method effectively reduced the residual stress caused by the wide butt welding during the construction.