Search Results (7)

This study investigates modular low-rise shear walls by designing and fabricating four in-plane loaded specimens at a scale ratio of 1:2.7. Quasi-static low-cycle reversed loading tests combined with numerical simulations were systematically conducted to examine the effects of the type and location of post-cast strips on the seismic performance of shear walls. The experimental program comparatively analyzed crack development patterns, failure modes, and seismic performance indices of specimens with four construction configurations: without post-cast strips, with only a horizontal post-cast strip, with a horizontal post-cast strip combined with an eccentrically placed vertical post-cast strip, and with a horizontal post-cast strip combined with a centrally placed vertical post-cast strip. The results indicate that specimens without post-cast strips exhibit uniformly distributed and highly penetrative cracks, characterized by typical global shear failure. The horizontal post-cast strip restricts downward crack propagation, leading to crack concentration above the post-cast strip, whereas the combined arrangement of horizontal and vertical post-cast strips promotes dispersed crack development and significantly alleviates excessive local damage concentration. The specimen with a centrally located vertical post-cast strip exhibited the best overall seismic performance, characterized by full hysteretic curves, the largest cumulative energy dissipation, and the most gradual stiffness degradation, whereas the specimen with only a horizontal post-cast strip showed relatively poor energy dissipation capacity and ductility. The finite element model established based on the experimental results accurately reproduces the mechanical responses and failure characteristics of all specimens, validating the mechanism by which post-cast strips improve wall performance through stress dispersion and crack development regulation. The findings demonstrate that a rational arrangement of post-cast strips, particularly the adoption of a centrally placed vertical post-cast strip, can effectively enhance the seismic performance of modular low-rise shear walls. Full article

This paper investigates the seismic performance of thin-walled stiffened steel square box columns, modeling bridge piers subjected to unidirectional cyclic lateral loading with a constant axial load, focusing on local, global, and local-global interactive buckling phenomena. Initially, the finite element model was validated against existing experimental results. The study further explored the degradation in strength and ductility of both thin-walled and compact columns under cyclic loading. Thin-walled, stiffened steel square box columns exhibited buckling near the base, forming a half-sine wave shape. The research also addresses discrepancies from different material models used to analyze steel tubular bridge piers. Analysis using a modified two-surface plasticity model (2SM) yielded results closer to experimental data than a multi-linear kinematic hardening model, particularly for compact sections. The 2SM, which accounts for cycling within the yield plateau and strain hardening regime, demonstrated enhanced accuracy over the multi-linear kinematic hardening model. Additionally, a parametric study was conducted to assess the impact of key design parameters—such as width-to-thickness ratio (R_f), column slenderness ratio (λ), and magnitude of axial load (P/P_y)—on the performance of thin-walled stiffened steel square box columns. Design equations were then developed to predict the strength and ductility of bridge piers. These equations closely matched experimental results, achieving an accuracy of 95% for ultimate strength and 97% for ductility. Full article

Local ice pressure refers to the ice pressure exerted on a very small area of a structure during ice failure. The existence of high-pressure zones may lead to local deformation and damage to ice-resistant structures, posing a serious threat to the overall structural stability. This study simulates the interaction between sea ice and structures through model tests, analyzing the timing of extreme local ice pressures. The results show that at low loading speeds, there is a 50% probability that the extreme local ice pressure occurs at the peak of the global ice force, while at high loading speeds, this probability drops to around 25%. Further investigation into the relationship between the global ice force peak, ice thickness, loading speed, and local area with local ice pressure amplitude reveals that the local ice pressure amplitude decreases with increasing loading speed and increases with ice thickness. Based on the area averaging method for square regions, the relationship between local ice pressure amplitude and local area is studied, showing that ice thickness, local width, and loading speed all influence the pressure–area relationship. Based on the square area averaging method, the relationship between the local ice pressure amplitude and the local area was studied. It was found that a linear relationship exists between the power function coefficient of local ice pressure–area and the thickness-to-width ratio. Compared to brittle failure, the local ice pressure amplitude under ductile failure of the ice sheet is more significantly affected by ice thickness. This study provides a foundation and reference for the analysis of ice-resistant performance and structural design of polar marine engineering structures. Full article

Withstanding extreme events is increasingly a significant challenge for the construction industry. Where civil infrastructures remain using traditional concrete, which has low tensile strength, poor durability, and weak crack resistance, in this regard, ultra-high-performance concrete (UHPC), with its outstanding mechanical properties and high strength, offers the prospect of wide application. This advanced technology allows for the fabrication of thin and light-dimensional structures to accelerate construction while increasing corrosion resistance to minimize maintenance intervention and extend the service life of the infrastructures. Despite this, UHPC is less eco-friendly due to consuming more cement than the usual material, which requires replacement materials, such as silica fume (SF) and rice husk ash (RHA), which are readily available from other local material production. This study proposes an experimental approach to assess the influence of SF and RHA content on the properties of UHPC. Different SF and RHA compositions will be adjusted to analyze their effects on slump flow, compressive strength, flexural strength, tensile strength, and the stress–strain relationship in UHPC tension testing. Based on the results, the most effective ratio is RHA replacing 50% of the SF in the UHPC mixture. Specialized tensile experiments reveal enhanced tensile strength with judicious RHA incorporation at 5-day and 28-day stages, particularly in initial crack and damage conditions. Stress–strain curves for 5% to 15% RHA samples show increased ductility, indicating that optimal RHA-SF ratios enhance UHPC cracking characteristics. Based on the results, a discussion on the appropriate proportions for utilizing most local materials will be derived, especially for regions of Vietnam. It is evaluated as a feasible and promising solution to reduce greenhouse gas emissions threatening global climate change. Full article

Shear-keyed inter-modular connections (IMCs) are integral components of high-rise modular steel structures (MSSs), providing robust interconnectivity to support grouped tubular columns across modules, thereby introducing column discontinuities and distinctive structural behavior. This study conducted a comprehensive numerical assessment and theoretical analysis of the axial compression behavior of grouped tubular columns based on a validated finite element model (FEM), which captured the member-to-structural level behavior of steel hollow section (SHS) columns and accommodated geometric imperfections. An FEM was initially developed and validated using 28 axial compression tests documented in the literature, comprising 15 tests on cold-formed and 13 on hot-rolled steel hollow section (SHS) columns. The primary parameters explored in tests included material properties (stainless/carbon), processing methods (cold-formed/hot-rolled), cross-section sizes (D/B), cross-sectional or member slenderness ratios (D/t_c, B/t_c, or L_c/r), and the number of columns (1, 7, and 11). A comprehensive parametric numerical study involving 103 grouped tubular column FEMs then investigated the influence of initial imperfection, shear-key height (L_t), thickness (t_t), steel tube length (D), width (B), thickness (t_c), and height (L_c) alongside the effects of space between tube and key, and the gap between tubes. The results indicated that the load-shortening behavior of the grouped columns consists of linear elastic, inelastic, and recession stages. The failure modes observed primarily displayed an S-shaped pair of inward and outward local buckling on the outer sides and double S-shaped local buckling on the interior sides. The buckling arose near the shear key or at 1/4 or 1/2 of the column height. None of the considered models experienced global buckling. Increasing t_t, L_t, t_c, D, or B enhances strength and stiffness, while L_c or L_c/r linearly affects stiffness and ductility. The columns’ nominal axial strength was reduced because of the shear keys, which decreased compression yielding and caused localized elastic buckling. Subsequently, the theoretical analysis revealed that the design codes do not capture this behavior, and thus, their capacity estimate yields inaccurate findings. This discrepancy renders existing code prediction equations, including those from Indian (IS800), New Zealand (NZS400), European (EC3:1-1), Canadian (CSA S16), American (AISC360-16), and Chinese (GB50017) standards, as well as the model proposed by Li et al., non-conservative. To assure conservative results, the paper recommended modification of existing standards and proposed prediction equations based on a fourth-order differential equation that describes the actual behavior of modular steel columns grouped with shear keys. The proposed design approach accurately predicted the axial compression capacity of modular steel-grouped columns, proving conservative yet effective. This provides valuable data that could transform design and construction techniques for MSSs, extending to various column and IMC forms through adaptable design parameters. This enhancement in structural performance and safety significantly contributes to the advancement of modular construction practices. Full article

Over the last century, the seismic behavior of reinforced concrete (RC) beam–column joints has drawn many researchers’ attention due to their complex stress state. Such joints should possess sufficient capacity and ductility to ensure integrity and safety when subjected to cyclic loading during seismic events. In the literature, while most studies have focused on the behavior of concentric beam–column joints, few studies investigated the response of eccentric beam–column joints, in which the beam’s centerline is offset from the centerline of the column. Recent earthquakes demonstrated severe damage in eccentric beam–column joints due to their brittle torsional behavior, which may threaten the ductility required for the overall structural performance. To investigate the effect of brittle failure on the strength, ductility, and stability of eccentric beam–column joints, nonlinear finite element (FE) models were developed and validated. The FE model was employed to study the effect of some geometric parameters on the global and local behaviors of beam–column joints, including the joint type (exterior and interior), the column aspect ratio, and the joint aspect ratio. The results show that the joint aspect ratio, which is the ratio of beam-to-column depth, has a predominant effect on the failure behavior of the joint. Additionally, the increase in column aspect ratio alters the failure mode from brittle joint shear failure to ductile beam-hinge, although there is an increase in the joint torsional moment. The current study also showed that interior joints exhibited a higher out-of-plane moment as well as more extensive column torsion cracks compared to exterior joints. Full article

A numerical investigation regarding ductility evaluation of steel buildings with moment resisting steel frames is conducted. Bending (µ_Lϕ) and tension (µ_Lδ) local ductilities as well as story (µ_S) and global ductilities are studied. Global ductility is calculated as the mean values of story ductilities (µ_GS) and as the ratio of the maximum inelastic to yielding top displacements (µ_Gt). The ductility capacity is associated to drifts of about 5%. Ductility values significantly may vary with the strong motion, ductility definition, structural element, story number, type of analysis, and model. µ_Lϕ is much larger for beams than for columns. Even though the demands of µ_Lδ are considered an important issue they are less relevant than µ_Lϕ. µ_S is much smaller than µ_Lϕ for beams. µ_GS for dynamic analysis give reasonable values, but µ_Gt does not. µ_Lϕ, µ_S and µ_GS obtained from pushover are larger than those obtained from dynamic analysis and unlike the case of dynamic analysis, µ_Lϕ tend to increase with the story number showing an opposite trend. Considering that: µ_Gt for dynamic analysis results in unreasonable values, pushover analysis does not consider energy dissipation, the strong column–weak beam (SCWB) concept was followed in the model designs, and µ_Lδ is not relevant in framed steel buildings, the ratio (R_LG) of global to local ductility capacity is calculated as the ratio of µ_GS to µ_Lϕ of beams, for dynamic analysis. A value of 1/3 is proposed. Thus, if bending local ductility capacity is stated as the basis for the design, the global ductility capacity can be easily estimated. Full article