Full-Range Stress-Strain Curves for Aluminum Alloys

[国外交通期刊数据库] 作者:Yun, Xiang;Wang, Zhongxing;Gardner, Leroy

摘要:Aluminum alloys are being increasingly used in a wide range of construction applications owing to their sound mechanical properties, lightness in weight, strong corrosion resistance, ability to be formed into complex and efficient cross-sectional shapes, and natural aesthetics. Aluminum alloys are characterized by a rounded stress-strain response, with no sharply defined yield point. Such behavior can be accurately represented using Ramberg-Osgood-type equations. In the present study, use of a two-stage Ramberg-Osgood model to describe the full-range stress-strain behavior of aluminum alloys is proposed and, following careful analysis of a comprehensive database of aluminum alloy coupon test data assembled from the literature, standardized values or predictive expressions for the required input parameters are derived. The experimental database includes over 700 engineering stress-strain curves obtained from 56 sources and covers five common aluminum alloy grades: 5052-H36, 6061-T6, 6063-T5, 6082-T6, and 7A04-T6. The developed model is shown to be more accurate in predicting the full-range stress-strain response of aluminum alloys than existing expressions, and is suitable for use in the analytical modeling, numerical simulation, and advanced design of aluminum alloy structures. (C) 2021 American Society of Civil Engineers.

Shear Strength of End Panels in Steel Plate Girders

[国外交通期刊数据库] 作者:Kim, Dong-Won;Uang, Chia-Ming

摘要:Plate girders, usually characterized by having large depth-to-web thickness ratios, have been widely used for long-span applications in bridges and buildings. US design provisions (AISC specifications for building design and AASHTO specifications for bridge design) permit the strength contribution from tension-field action after web buckling in calculating the design shear strength of interior panels, but not exterior panels. Testing of four large-size steel plate girders demonstrated a much higher shear resistance of end panels than those predicted by code provisions. Based on the failure mode observed from both testing and finite element simulation, an analytical model was developed to simulate the collapse mechanism. Plastic analysis was used to derive a shear strength equation. This equation, similar in format to that used in current design codes for interior panels, includes a parameter beta(v) to account for the contribution of partial tension-field action. (C) 2021 American Society of Civil Engineers.

Flexural Performance of UHPC-Concrete-ECC Composite Member Reinforced with Perforated Steel Plates

[国外交通期刊数据库] 作者:Huang, Bo-Tao;Dai, Jian-Guo;Weng, Ke-Fan;Zhu, Ji-Xiang;Shah, Surendra P.

摘要:A novel reinforced concrete structural member comprising ultrahigh-performance concrete (UHPC) and engineered cementitious composite (ECC) was proposed for use in underground structures, such as prefabricated utility tunnels. In this composite member, UHPC was used as the exterior (i.e., soil side) protective layer to prevent the penetration of water and corrosive agents, and ECC was used as the interior (i.e., service environment side) protective layer to improve the member's crack-control capacity and fire resistance. Ordinary concrete was filled between the UHPC and ECC layers. The composite member was reinforced with perforated steel plates to achieve strong mechanical interaction between the composite materials and to ensure structural integrity. The proposed composite was experimentally characterized as follows. The tension-stiffening effect in ECC panels with a perforated steel plate was evaluated using direct tensile tests. The flexural behavior of the reinforced UHPC-concrete-ECC members was characterized with four-point bending tests. The failure processes of the composite members were analyzed via the digital image correlation (DIC) method. Finally, a simplified theoretical method was developed to estimate the yield and ultimate load-carrying capacities of the composite member, and the estimated results showed good agreement with the test results. Overall, the proposed composite member had favorable mechanical performance and durability due to the strategic use of UHPC and ECC. (C) 2021 American Society of Civil Engineers.

Load-Carrying Capacity of Corroded Gusset Plate Connection and Its Repair Using CFRP Sheets

[国外交通期刊数据库] 作者:Pham, Ngoc Vinh;Miyashita, Takeshi;Ohgaki, Kazuo;Okuyama, Yusuke;Hidekuma, Yuya;Harada, Takuya

摘要:Recently, several events involving the corrosion-induced damage of gusset plate connections of steel truss bridges have been reported worldwide. In this study, the remaining load-carrying capacity of a corroded gusset plate connection was evaluated through loading tests and finite element method (FEM) analyses using a model approximately 50% of the size of an actual gusset plate connection. Two potential forms of corrosion, that is, weld and cross-sectional corrosion, on the gusset plate were considered in order to investigate the reduction in the load-carrying capacity. Then, parametric FEM analyses were conducted to determine the effect of the corrosion level on the remaining load-carrying capacity of a specimen model and a full-scale model of an actual connection. The loading tests and parametric FEM analyses indicated that with increases in the dimensions of the corroded sections, the load-carrying capacity of the gusset plate connections exhibited nearly similar linear decreases. Furthermore, the effectiveness of a repair method for the corroded gusset plate connection using carbon fiber-reinforced plastic (CFRP) sheets was investigated. The loading tests were conducted considering the area, direction, and location of the bonded CFRP sheets. As a result, this study proposed an appropriate repair method using CFRP sheets that could help recover the load-carrying capacity and improve the deformation performance of corroded gusset plate connections. (C) 2021 American Society of Civil Engineers.

Reducing Processing Time of Nonlinear Analysis of Symmetric-Plan Buildings

[国外交通期刊数据库] 作者:Reyes, Juan C.;Avila, William A.;Kalkan, Erol;Sierra, Armando

摘要:Nonlinear response history analysis has been a powerful tool in performance-based earthquake engineering for validating the proposed design of new structures or evaluating existing ones. When it is applied to structural systems with a large number of degrees of freedom, such as three-dimensional (3D) models of tall buildings, bridges, or dams, the analyses can be time-consuming. The prolonged computing times become more prominent in parametric studies or in incremental dynamic analyses. In order to reduce the computation time, this study proposes a practical method-a reducing time steps (RTS) procedure-whereby leading and trailing weak signals in the input acceleration record are trimmed, and the remaining record is downsampled. The test results based on several different 3D computer models of reinforced-concrete idealized structures demonstrate that the RTS method is practical, and it provides estimates of engineering demand parameters such as peak values of story drift, floor acceleration, and floor velocity within 10% of the results obtained by using the original records. The RTS procedure was further validated on three symmetric-plan steel buildings with 5, 9, and 15 stories. For all analyzed cases, the average reduction in computational time was around 50%. (C) 2021 American Society of Civil Engineers.

Probabilistic Models and Fragility Estimates for Unreinforced Masonry Walls Subject to In-Plane Horizontal Forces

[国外交通期刊数据库] 作者:Iannacone, Leandro;Andreini, Marco;Gardoni, Paolo;Sassu, Mauro

摘要:Unreinforced masonry (URM) buildings make up a significant portion of the built environment, with hollow clay being the predominant choice for the units. The capacity of URM buildings is a function of the capacity of its walls, both to vertical and horizontal forces. However, URM is particularly vulnerable to the effect of horizontal forces due to the low tensile strength of the mortar that holds the units together. URM walls are subject to significant in-plane horizontal forces during seismic events, so that a proper quantification of the capacity of URM walls to this type of forces is required. The models in design codes are often conservative and do not capture the uncertainties required for estimating the failure probability of URM walls. This paper develops probabilistic capacity models for URM walls with hollow clay units subject to horizontal in-plane forces. The models are developed considering diagonal cracking, flexural/rocking, and sliding failure as possible failure modes. The models are constructed starting from existing physics-based models that attempt to capture the underlying physics, and then developing correction terms that improve the accuracy of the models and remove the inherent bias. Unknown parameters for the proposed models are calibrated using a Bayesian updating approach. The proposed models are probabilistic and capture the relevant uncertainties. The proposed models are used to assess fragility functions of example URM walls subject to horizontal in-plane forces. The comparison of the fragility functions shows the effect of selected variables. (C) 2021 American Society of Civil Engineers.

Quantifying the Fatigue Material Properties of UHPFRC with Steel Microfibers at Cracks

[国外交通期刊数据库] 作者:Sepulveda, Barbara D. G.;Visintin, Phillip;Oehlers, Deric J.

摘要:The addition of steel fibers to concrete in ultrahigh-performance concrete (UHPC) to form ultrahigh-performance fiber-reinforced concrete (UHPFRC) has been shown to have a great benefit by substantially increasing the flexural capacities and ductilities at the ultimate limit state and reducing crack widths and increasing flexural rigidities at the serviceability limit state. This is because the fibers bridge a crack and consequently allow tensile stresses across the crack. Tests also have shown that tensile cyclic loads applied across a crack can reduce these benefits by allowing the crack to widen through a gradual debonding of the fibers. To quantify the behavior of UHPFRC post cracking, the fatigue behavior of steel microfiber concrete at a crack was studied through 33 tensile fatigue tests on precracked UHPFRC and 6 monotonic tests. An approach for processing the results based on the increase in crack width per cycle, that is the incremental set, was developed and can be applied to any UHPFRC that exhibits debonding. Three distinct cyclic behaviors were identified and quantified: no incremental set, such that there is no quantifiable damage due to cyclic loading; the incremental set is constant, such that there is quantifiable damage; and a rapid unstable increase in the incremental set. (C) 2021 American Society of Civil Engineers.

Model Type Effects on the Estimated Seismic Response of a 20-Story Steel Moment Resisting Frame

[国外交通期刊数据库] 作者:Lachanas, Christos G.;Vamvatsikos, Dimitrios

摘要:Finite-element models of varying sophistication may be employed to determine a building's seismic response with increasing complexity, potentially offering a higher fidelity at the cost of the computational load. To account for this effect on the reliability of performance assessment, model-type uncertainty needs to be incorporated as distinct to the uncertainty related to a given model's parameters. At present, only placeholder values are available in seismic guidelines. Instead, we attempt to quantify them accurately for a modern 20-story steel moment-resisting frame. Different types of three-dimensional (3D), two-dimensional (2D) multibay, and 2D single-bay multidegree-offreedom models are investigated, together with their equivalent single-degree-of-freedom ones, to evaluate the model dependency of the response both within each broad model category, as well as among different categories. In conclusion, ensemble values are recommended for the uncertainty in each model category showing that for the perfectly-symmetric perimeter-frame P-Delta. sensitive building under investigation, the uncertainty stemming from 3D versus 2D or distributed versus lumped plasticity models is lower than the governing record-torecord variability. (C) 2021 American Society of Civil Engineers.

Simplified Nonlinear Simulation of Rectangular Concrete-Filled Steel Tubular Columns

[国外交通期刊数据库] 作者:Tao, Zhong;Katwal, Utsab;Uy, Brian;Wang, Wen-Da

摘要:In detailed three-dimensional (3D) finite-element modeling, two-dimensional and/or 3D elements are widely used because of their high accuracy and ease of use despite the high computational cost. In contrast, simplified modeling based on fiber beam element (FBE) formulation is preferred for developing macro models to simulate structural frames due to its simplicity and computational efficiency. As for the FBE simulation of concrete-filled steel tubular (CFST) columns, its accuracy largely depends on the input steel and concrete material models, which should implicitly consider the material nonlinearity and interaction between the steel and concrete components. The authors have previously developed a FBE model for circular CFST columns, and this paper is a continuation of the previous work. In this paper, uniaxial effective stress-strain relationships are developed for the steel and concrete materials in rectangular CFST columns based on rigorous analysis of data generated from 3D finite-element modeling of stub columns. Thus, the material models have implicitly considered the effects of yielding and local buckling of the steel tube and passive confinement to the concrete. Meanwhile, the size effect is also considered in the concrete model. The accuracy of the proposed material models is verified against a database of rectangular CFST stub columns covering a wide range of material and geometric parameters. The developed material models are further used to simulate rectangular CFST slender columns and beam-columns, and a reasonably good agreement is achieved between the experimental and predicted load-deformation curves. (C) 2021 American Society of Civil Engineers.

Contribution of Partition Walls in Lateral Load-Resisting Systems of Low-Rise Light Wood Frame Buildings

[国外交通期刊数据库] 作者:Niederwestberg, Jan;Daneshvar, Hossein;Chui, Ying Hei;Chen, Zhiyong

摘要:Prescriptive design is a common practice in North America for low-rise light wood frame buildings. The prescriptive wood-based shear wall details provided in building codes to resist lateral loads were largely derived based on a combination of historical performance and engineering analysis. Inherent within the historical performance assumption is the presence of certain elements such as internal partitions that contribute to direct load resistance and structural redundancy. This inherent assumption is sometimes challenged by design engineers and proponents of alternative lateral load-resisting systems. In an attempt to showcase the contributions of the partition walls, a number of archetypes with various quantities of partitions were analyzed using a finite-element program. In the finite-element models, the wood-based structural shear walls and partition walls with gypsum wallboard were modeled as macroelements, with mechanical properties obtained from previous tests. Assumptions were made for the diaphragm and connection stiffness values. The results show a significant contribution of the partition walls to the lateral load resistance of light wood frame buildings. Partition walls accounted for 55%-71% of the overall lateral resistance of the evaluated buildings. Furthermore, diaphragms and wall-to-diaphragm connections contribute significantly to the overall behavior of the structures. (C) 2021 American Society of Civil Engineers.