Bracing Demand in Axially Loaded Cold-Formed Steel Stud Walls

The problem of determining adequate bracing for multiple studs in a wall with similar imperfections is addressed. Previous studies have determined the necessary brace strength and stiffness required to adequately brace a single axially loaded cold-formed steel stud and this information has been incorporated into design standards. Using elastic nonlinear frame analysis software, the required bracing strength and stiffness demand for a single compression member that was derived by Winter and recommended by previous studies was replicated. The model was then expanded to include walls with up to 30 studs, braced at both the midpoint and third point. For these models the required brace stiffness and the resulting brace forces were recorded and compared to the requirements for a single stud. Analysis of the data indicates that the required brace strength accumulates directly as to the number of braced studs. The required brace stiffness for bracing multiple studs may be determined through the use of a simple second-order equation.     

Wall Stud-to-Track Gap: Experimental Investigation

Because of an increasing interest in the use of cold-formed steel for commercial and residential framing, both design and installation guidelines are needed. The wall framing, which typically consists of axial load bearing C-section studs, is laterally braced and attached at the bottom and top of the wall to a track section. The common bottom and top attachment consists of the wall stud and track of nominally the same cross-section depth. Because the nominal depths of the C-section and the track are similar, a tight connection is often not achieved and a gap occurs. The Standard for Cold-Formed Steel Framing—General Provisions specifies that the gap between the wall stud and track in a wall assembly must not exceed 1/8?in. This gap dimension is consistent with the gap specified by ASTM C 1007. The value of 1/8?in. is based on industry experience and practice but had not been experimentally verified. To explore both the stud-to-track connection strength and the aesthetic concerns associated with a gap between the axial load bearing stud and the track in a typical cold-formed steel wall assembly, a test program was initiated at the University of Missouri-Rolla. Based on the findings of the 54 wall assembly tests and short column tests performed in this experimental study, design guidelines are proposed for a typical wall stud assembly.     

Static Behavior and Theoretical Model of Stud Shear Connectors

Stud shear connectors are the most widely used shear connectors in steel-concrete composite beams. The composite action of steel beam and concrete slab is effected by the stud shear properties directly. Thirty push-out tests on stud shear connectors were conducted to investigate the effects of stud diameter and height, concrete strength, stud welding technique, transverse reinforcement, and steel beam type on stud failure mode, load versus slip curve, and the shear bearing capacity. Based on the push-out test results, the stud shear mechanism was analyzed, a new expression of stud load-slip relationship was put forward, and a calculation model of stud shear bearing capacity was proposed taking into account the influences of stud diameter and height, material strength, and elastic modulus. Compared with existing models, the computed shear bearing capacities of the proposed calculation model had a better match with the experimental values.     

Use of Precast Concrete Walls for Blast Protection of Steel Stud Construction

This research study examines the use of a precast concrete panel system for blast protection of facilities with exterior light gauge metal stud walls. The structural retrofit is designed for the specific case where internal operation of the facility cannot be interrupted. To meet this design requirement, a series of precast concrete panels are installed exterior to the building envelope with connections to the foundation at ground level and to the steel building frame at upper floor levels. To validate the retrofit concept, two explosive detonations representing relatively low and high blast threat levels are examined. An exterior insulation and finishing system (EIFS) clad stud wall and a precast concrete protected stud wall are examined under each demand level. The measured responses of both systems are compared with each other and with basic dynamic predictive models. In addition, a finite element study of the connection is conducted to estimate support demands for the blast retrofit. The research results show that the precast wall system provides effective protection of the exterior wall. The research also shows that EIFS clad metal stud wall systems retain significant resilience under blast demands. The dynamic responses of the systems are predictable using standard elastic-plastic dynamic modeling assumptions.     

Response of Bonded Membrane Retrofit Concrete Masonry Walls to Dynamic Pressure

This paper describes the development of analytical models used to predict the response of bonded membrane retrofit concrete masonry walls subjected to out-of-plane impulse pressure loads. Full scale tests have shown significant improvement in the resistance of unreinforced concrete masonry walls retrofitted by membrane materials. The majority of the membrane retrofit concrete masonry walls survived compared to their unretrofitted counterparts that collapsed. Polymer membrane retrofit materials may be sprayed on, trowled on, or attached with adhesives to the tension face of the wall. Other membrane materials such as thin steel or aluminum sheets may be attached to the tension face of the wall using expansion screws or other structurally sound methods. Resistance functions previously presented by the writers for membrane retrofit concrete masonry walls are used in the development of the response. Single-degree-of-freedom equations are developed to predict the response of these walls to impulse pressure and the results of the analysis are compared with available full-scale tests.     

Concept and Finite-Element Modeling of New Steel Shear Connectors for Self-Centering Wall Systems

Self-centering precast concrete walls have been found to provide excellent seismic resistance. Such systems typically exhibit low energy dissipation, requiring supplementary dissipating components to improve their seismic performance. Mild steel shear connectors can provide an economical energy dissipating element. The design and analysis of steel shear connectors for a new precast wall system has been undertaken. A series of finite-element analyses were conducted to investigate the behavior of different types of connectors. Emerged from these analyses is a oval-shaped connector (O-connector) that provided satisfactory force-displacement behavior and appeared well suited for the new wall system in high seismic regions. An extensive experimental test program was then conducted to verify the performance of the chosen O-connector, which confirmed the expected response with sufficient energy dissipation. The experimental data demonstrated good correlation with the finite-element model developed, providing satisfactory confidence in the finite-element technique used for the development of the different connectors.     

Modeling the Nonlinear Behavior of Concrete Masonry Walls Retrofitted with Steel Studs under Blast Loading

This paper presents the results of an analytical investigation of one-way unreinforced masonry (URM) walls retrofitted with externally anchored steel studs and subjected to blast loads. Using the wall geometrical and material properties, deflected shape, and crack pattern as input, a nonlinear model is developed to predict the inward force-displacement relationship of the retrofitted walls. In addition, using a rigid body analysis, a simple bilinear force-displacement relationship is developed to model the outward force-displacement relationship of the walls. Utilizing these two force-displacement relationships (resistance functions), a generalized single-degree-of-freedom (SDOF) model is developed to capture the nonlinear out-of-plane dynamic response of the retrofitted walls under blast loads. The SDOF model captured the experimentally observed displacement responses of the tested walls with reasonable accuracy. The model was also used to investigate the influence of block thickness, wall slenderness ratio, blast load intensity, and blast pulse shape on the out-of-plane dynamic response of retrofitted walls. The results demonstrated that anchored steel-stud systems could significantly enhance the out-of-plane capacity of the retrofitted walls by increasing their out-of-plane capacity and reducing their displacement.     

Introduction of a Panelized Brick Veneer Wall System and Its Building Science Evaluation

This paper introduces a panelized brick veneer over steel stud backup wall system to address some of the shortcomings of conventional systems. Thermal and hygrothermal analyses of the proposed wall system with different stud gauges and arrangements are discussed. The movement joint design aspects, a pressure moderation performance evaluation, the simulated wind-driven water penetration results, and an example cost analysis are also presented. This study provides information about some of the attributes of the proposed system such as crack resistance and water penetration potential as well as the pressure moderation aspect. Some of the issues that need consideration for the practical application of the system are also described.     

Bearing Strength of Slabs on Grade Supporting a Cold-Formed Steel Wall in Low-Rise Building

The main objective of this research project was to develop a better understanding of the bearing strength of slabs on grade supporting load-bearing walls made of cold-formed steel studs and tracks used in residential and commercial multistory constructions. A total of 60 specimens were manufactured with four different configurations of stud-track assembly: single stud, single-stud wall, back-to-back, and back-to-back wall. The test results showed that the bearing strength was affected by the configurations of the stud-track assembly, and that the bearing strength gradually increased as the stud-track assembly was located at the inner side from the edge of the slab due to the confinement effect of the surrounding concrete. An analytical study using a finite-element model was performed to develop the analytical equations used to predict the bearing area of the stud-track assembly. Design guidelines were proposed based on the test results and the analytical study, which included the equations to compute the design bearing capacity of slabs on grade at varying distances from the edge of the slab to the stud-track assembly.     

Performance of Unreinforced Masonry Walls Retrofitted with Externally Anchored Steel Studs under Blast Loading

Six full-scale concrete masonry walls were tested under free-field blast loading using different charge sizes up to 250?kg of ammonium nitrate/fuel oil (ANFO) and at a constant stand-off distance of 15.0?m to cover a wide range of expected damage levels. Five walls were retrofitted with cold-formed steel studs anchored to the wall backs and were compared to the remaining as-built wall. Significant enhancement to the out-of-plane blast resistance of the retrofitted walls, compared to the as-built wall, was observed. This enhancement is attributed to the development of a tied-arch action in the retrofitted walls in which the masonry forms a compression strut while the steel studs serve as the tie. A simplified single-degree-of-freedom model was used to analyze the experimental results, and the model results agreed well with the observed damage levels and the resistances of the walls. In addition, the effectiveness of the proposed retrofit technique was evaluated in terms of strength enhancement and wall deflection reduction. The test results were also compared with those predicted by available blast damage assessment models for unreinforced masonry walls. However, it was found that available models, which do not account for the tied-arch mechanism, greatly underestimate the actual blast capacity of the retrofitted walls because of the assumption of a tensile flexural failure mode. Additionally, the proposed retrofit technique shifts the mode of failure from flexure to shear.     

Failure of Cold-Formed Steel Beams during Concrete Placement

During a concrete placement on the second story of a building under construction, the supporting cold-formed steel beams collapsed. Four workers were injured. The collapse occurred while concrete was being placed onto steel decking on the second floor of the structure. Cold-formed steel beams, without shoring, supported the steel decking. Analysis of the steel beams under the weight of concrete and workers using the applicable American Concrete Institute and American Iron and Steel Institute documents indicated that the beams were overstressed for construction loads. After the collapse, part of the structure was rebuilt using thicker beams. For the reconstruction, the slab was shored. Designing with cold-formed steel requires knowledge of failure modes that can often be safely ignored with hot-rolled steel, such as local buckling. Engineers designing with this material should take care to obtain the proper codes and design documents.     

Exact Solution for Dynamic Response of Multi-Degree-of-Freedom Bilinear Hysteretic Systems

An exact solution technique for the response of a bilinear hysteretic multi-degree-of-freedom system subjected to arbitrary dynamic loadings is proposed. Each function in the loading vector is represented by a piecewise interpolation polynomial. By using the modal superposition method and the Duhamel integral procedure on each branch of the force-displacement relationship and matching transitional conditions, one can obtain a closed-form solution. When the system is subjected to such piecewise polynomial loadings as an earthquake acceleration, which usually can be represented by a series of straight line segments, an exact result can be obtained. Thus the proposed method can provide much higher accuracy, and requires less computational effort than the traditional step-by-step integration solution technique. The reason for these advantages is discussed and the related formulas are provided.     

Ti-IF钢动态再结晶模型

通过Thermecmastor-Z热模拟实验机对Ti-IF(无间隙原子)钢(%:0.009C、0.017Si、0.13Mn、0.012P、0.013S、0.05Ti、0.025Als)在750℃、850℃和变形速率0.1,1,20s^-1下进行单道次压缩变形实验。得出Ti-IF钢加工硬化率-应变曲线、动态再结晶状态图和动态再结晶体积分数方程。实验结果表明,对于无明显峰值应变的应力-应变曲线,采用加工硬化率方法确定峰值应变和稳态应变是一种有效的方法。     

B30MnSi钢的动态再结晶行为

采用Gleeble1500热模拟试验机对B30MnSi钢(%:0.32C,1.04Mn,0.85Si,0.019P,0.009S)进行变形温度为850～1000℃,应变速度为0.1～101/s的压缩变形试验,以研究该钢的动态再结晶规律。并通过回归分析得出峰值应力σm,应变εp,动态再结晶临界应变εc与温度补偿变形速率因子Z之间关系式为σm=16.689Ln(Z)-347.41;εp=0.0474Ln(Z)-1.1023;εc≈0.0393Ln(Z)-0.915。     

高压水射流清洗钢板系统参数分析与研究

钢板表面的清洗效果对埋弧焊管焊接质量有着重要的影响,所以在焊接前通常需要将钢板表面的污垢清洗干净。而影响高压水射流清洗钢板系统清洗效果的因素有很多,主要对高压水射流清洗钢板效果有重大影响的喷嘴布置、喷嘴水射流打击力和系统优化设计进行了分析研究。     

Role of Insulation Effectiveness on Fire Resistance of Steel Structures under Extreme Loading Events

Fire performance of steel structures is highly dependent on the effectiveness of applied fire insulation. However, insulation materials are susceptible to damage under extreme loading events. A state-of-the-art review on the role of insulation damage on fire resistance of steel structures is presented. Parametric studies on a six-story steel-framed building were carried out to illustrate the effect of insulation damage on fire response of a steel structure. In the analysis, realistic fire scenarios, loading, and failure criteria were taken into consideration. Analysis results indicate that the fire resistance of a steel-framed structure is significantly influenced by the extent of insulation loss, type of fire scenario, and level of lateral load. Insulation damage causes faster deterioration in the structural response of framed buildings under the combined effect of fire and lateral loading. The need for accounting for any insulation damage, arising under extreme loading events, in fire design of steel-framed structures is highlighted, and a performance-based design strategy incorporating fire resistance analysis is discussed.     

Dynamic Modeling of Pressure Reducing Valves

Models are currently available for representing the dynamical behavior of most water network components. Such models are relatively simple, accurate and can be easily solved. However, there is no generally accepted dynamic model of a pressure reducing valve (PRV). The key contributions of this paper are the development of several dynamic models—two phenomenological, one behavioral, and one linear—to represent the behavior of PRVs. The models vary in complexity but perform similarly. Experimental data is used to assess the accuracy of the models. The phenomenological models are derived from physical laws and provide an excellent but complex representation of a PRV. The behavioral model is simpler and sufficient for most practical purposes. The linear model does not take the needle valve setting (which controls the valve’s speed) into account and therefore has limited use.     

0.03Nb-0.15Ti微合金化低碳高强度钢的动态再结晶

通过Gleeble 1500热模拟试验机试验研究了Nb-Ti微合金化低碳钢（/%:0.06C,0.22Si,1.80Mn,0.03Nb,0.15Ti,≤0.007N,≤0.002S）10mm带钢在850~1100℃,以应变速率0.1~20.0 s^-1,总变形量75%单道次压缩变形时动态再结晶,由真应力-真应变曲线,结合加工硬化率曲线,得出动态再结晶临界应变0.4~0.7和完全再结晶应变量1.1~1.4。该钢的热变形激活能为618.225 kJ/mol。根据试验结果得到Zener-Hollomon方程和动态再结晶状态图,利用Johnson-Mehl-Avrami（JMA）方程法得到再结晶体积分数实际值,采用Epsilon-P模型对实验数据进行回归,得到试验钢的再结晶动力学模型。     

非调质钢38MnVS奥氏体动态再结晶的研究

研究了V-Ti微合金非调质钢38MnVS（/%:0.42C、0.76Si、1.33Mn、0.011S、0.013P、0.10V、0.02Ti）的奥氏体动态再结晶过程。通过Gleeble-3800热模拟试验机,研究了变形温度（950～1150℃）和变形速率(0.1～10s^-1)对38MnVS钢奥氏体动态再结晶过程的影响,并建立了Zener-Hollomon参数为变量的方程、动态再结晶尺寸模型和动态再结晶状态图。结果表明,变形温度越高,变形速率越低,发生动态再结晶的临界驱动力越小,动态再结晶越易进行;微合金非调质钢38MnVS动态再结晶激活能为Q_d=275.453 kJ/mol。     

舞钢低温高韧性压力容器用钢板

本文论述了舞钢开发的一系列低温高韧性压力容器用钢板的生产工艺和技术保证措施，客观地评价了钢板的实物质量水平，并提出今后进一步研究开发的设想。