AbstractDevelopment in ultra-high-performance fiber-reinforced concrete (UHPFRC) structural applications that has taken place over the last two decades has generated innovative concepts that could ...significantly impact the concrete construction practice. The transition from conventional concrete with brittle behavior to strain-hardening behavior in direct tension allows consideration of the design of innovative structural components and offers development of new techniques for rehabilitation. Building on experimental results of internally instrumented reinforcing bars, this paper investigates the impact of tensile characteristics of UHPFRC on the performance of lap splice connections using a refined three-dimensional (3D) finite-element (FE) model at rib scale and a 3D concrete constitutive model implemented in a computer program. The results show that the model reproduces with accuracy the experimental behavior of lap splice connections in UHPFRC in terms of maximum strength, splitting failure mode, crack pattern, steel stress distribution along the splice, and eventual loss of bond. Using the validated 3D nonlinear finite-element model, the influence of splice length and UHPFRC cover thickness are highlighted in a parametric study of corner and interior lap splices. The paper illustrates the methodology that can be adopted along with experimental results to develop guidelines for designing lap splice connection in UHPFRC.
AbstractThis paper presents key parameters that affect numerical modeling of steel frame structures for reliable collapse simulations. The collapse assessment is based on experimental data obtained ...from a full-scale shaking table collapse test of a 4-story steel moment frame and a blind numerical analysis contest that was organized in parallel with the collapse test. It is shown that (1) there is no clear advantage between three-dimensional (3D) and 2D analyses in the prediction of a sidesway collapse mechanism for buildings with a regular plan view as in the case of study; (2) the assumption of Rayleigh damping leads to better predictions of structural response compared with stiffness proportional damping; and (3) accurate prediction of collapse necessitates that P-Δ effects always be considered in the analysis. It is also proven that accurate simulation of steel component deterioration is a key factor for reliable prediction of collapse behavior. On the basis of a synthesis of experimental and analytical studies, a few collapse mitigation alternatives are investigated. In particular, the effects of the strong-column/weak-beam ratio and exposed base plates on the collapse capacity are assessed. It is notable that a combination of bending strength increase and delay of local buckling in first-story columns is most effective for the enhancement of seismic performance against collapse.
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Dostopno za:
DOBA, FGGLJ, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
AbstractResidual stress is one of the most important imperfections of steel structure members because of its significant effects on buckling behavior. To quantify the residual stresses in 420-MPa ...high-strength steel hot-rolled equal angle sections, an experimental study was conducted by using the sectioning method. The residual stress magnitudes and distributions for 15 sections were obtained, and the effects of the width-thickness ratios were clarified. Based on the test results, it was found that the ratio between the residual stress and the steel yield strength for 420-MPa steel equal angles was much smaller than that of normal strength steel angles; however, the distribution was analogous. The residual magnitudes significantly correlated with the width-thickness ratios of the legs. In addition, calculation formulas for the residual stress magnitudes were proposed in which the width-thickness ratios of the angle legs were taken into account, and three distribution models were established to be incorporated in the buckling analysis. The fundamental research and conclusions presented may provide useful experimental data and calculation methods for further studies on the residual stress and buckling behavior of high-strength steel members.
AbstractSteel concentrically braced frames inherently provide great strength and stiffness, and are widely used for seismic resisting systems in buildings. These include conventional buckling braced ...frames and buckling restrained braced frames. Although the latter can prevent brace buckling and provide ductile behavior, both types of braces provide no hysteretic damping at small drift levels and offer very limited post-yielding stiffness. This study proposes a new type of steel brace with a novel mechanism—the naturally buckling brace (NBB). The design combines high-strength and low-yield steels arranged in parallel with a specified initial eccentricity along the brace length, providing ductile seismic behavior. Six tests of various NBB models subjected to cyclic loading were conducted to examine the seismic performance of the proposed NBB. Two specimens out of the six achieved the characteristics intended for NBB. The test results showed that the NBB specimens with appropriate design parameters could achieve early yielding, or hysteretic damping, from around 0.11% story drift and prevent local buckling as well as deformation concentration up to a very large story drift (greater than 3%). A single NBB would provide an asymmetric hysteretic behavior, a large post-yielding stiffness in tension, and a ductile performance with stable energy dissipation. Further systematic studies of NBBs are needed to comprehensively evaluate the capacities and limitations of the NBBs, including the reliability of performance with repeated tests.
Wood-frame residential construction represents a major investment in the United States, which, when exposed to hurricanes, earthquakes, and other natural hazards, may sustain substantial damage. ...Although in many parts of the country one natural hazard dominates, in certain areas multiple hazards may pose a significant threat to buildings. Building design and construction practices should address the overall risk to residential construction from multiple hazards to achieve design strategies and risk levels that are consistent with occupant expectations and social objectives. This paper presents a framework for multihazard risk assessment using hurricane and earthquake hazards as an example. Structural reliability-based methods that describe natural hazard and structural system response probabilistically are essential for quantifying expected losses from natural disasters and for developing appropriate strategies to manage risk. The framework permits the main sources of uncertainty that affect building performance to be identified, and provides insight on strategies for effective multihazard mitigation efforts.
Many theoretical and experimental studies have been carried out on fiber-reinforced plastic (FRP)-confined circular concrete specimens, leading to a variety of models for predicting their axial ...compressive strengths. In this paper, a large test database assembled from an extensive survey of existing studies is presented and employed to assess available axial strength models for FRP-confined concrete. The test database is also deployed to examine the effect of various factors on the performance of FRP-confined concrete. This study shows that the confinement effectiveness of FRP based on reported test results depends little on unconfined concrete strength, size, and length-to-diameter ratio of test specimens and FRP type, but depends significantly on the accuracy of the reported tensile strength of the FRP. The inherent variation of unconfined concrete strength also causes some scatter of data at low confinement ratios. Using those test data with accurate FRP tensile strengths, only two of the nine existing models are found to give close predictions. A new simple model is finally proposed, based on the observation that a linear relationship exists between the confined concrete strength and the lateral confining pressure from the FRP.
Celotno besedilo
Dostopno za:
DOBA, FGGLJ, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
AbstractA curve-approximated hysteresis model of the lateral load-displacement behavior of steel bridge columns is proposed for nonlinear seismic response assessment of single-column-type bridges ...using single-degree-of-freedom (SDOF) analysis. Instead of multiple straight lines, a series of curves are adopted to precisely describe complicated force-displacement hysteresis behavior of the column. The P-δ effect, hardening effect in unloading-reloading hysteresis loops, deterioration of strength, and stiffness are taken into account. Parameters of proposed hysteresis model for three types of steel column specimens used in this study are calibrated by six quasi-static cyclic tests. To verify the accuracy of the proposed model, eleven pseudodynamic tests are conducted. By comparing the simulation and the test results, the differences between the predicted nonlinear seismic response using the proposed model and pseudodynamic tests are found to be, on average, 5% in maximum response displacement, 22% in residual displacement, and 4% in the amount of energy dissipation.
The computational assessment of system reliability of structures has remained a challenge in the field of reliability engineering. Calculation of the failure probability for a system is generally ...difficult even if the potential failure modes are known or can be identified, because available analytical methods require determination of the sensitivity of performance functions, information on mutual correlations among potential failure modes, and determination of design points. In the present paper, a method based on moment approximations is proposed for structural system reliability assessment that is applicable to both series and nonseries systems. The point estimate method is applied to evaluate the first few moments of the system performance function of a structure from which the moment-based reliability index and failure probability can be evaluated without Monte Carlo simulations. The procedure does not require the computation of derivatives, nor determination of the design point and computation of mutual correlations among failure modes; thus, it should be computationally effective for structural assessment of system reliability.
The nonlinear finite-element analysis of RC members subjected to cyclic loading requires complicated modeling and analytical techniques. In the present study, a simplified nonlinear analytical method ...using a truss model was developed. In the nonlinear truss model, a RC member was idealized by longitudinal, transverse, and diagonal truss elements. Each element was modeled as a composite element of the concrete and the reinforcing bar. Cyclic stress–strain relationships were developed in order to describe the nonlinear behavior of the composite concrete and reinforcing-bar elements. The nonlinear truss model was applied to existing test specimens with various reinforcing-bar layouts under various loading conditions. The results predicted by the nonlinear truss model were compared with the test results. The comparison revealed that the nonlinear truss model predicted the load-carrying capacity and energy dissipation of the test specimens with reasonable precision. However, to estimate the deformation capacity of the specimens, the compression softening of concrete struts and the buckling and fracture of the reinforcing bar must be predicted more accurately.
Celotno besedilo
Dostopno za:
DOBA, FGGLJ, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
