Response of Conventional Steel Stud Wall Systems under Static and Dynamic Pressure

This research effort focuses on the evaluation of existing design standards for cold-formed steel stud?walls and the development of retrofit wall systems. Full-scale wall systems are tested under uniform static pressure using a vacuum chamber. The resistance functions obtained are used to model the dynamic behavior of the walls and to predict performance under blast conditions. This paper focuses on defining the static resistance of nonload-bearing steel stud walls with slip track connections and their performance under external explosions. Simple modifications to existing design practice have significantly improved the blast performance of the steel stud walls. Maximum blast resistance is achieved by using steel angles connected to the studs and anchored to the floor and ceiling. The static and dynamic performances of five full-scale steel stud wall systems are presented in this paper.     

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.     

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.     

In-Plane Shear Behavior of Masonry Panels Strengthened with NSM CFRP Strips. I: Experimental Investigation

An experimental investigation was conducted to study the in-plane shear behavior of masonry panels strengthened with near-surface mounted (NSM) carbon fiber-reinforced polymer strips (CFRP). As part of the study four unreinforced masonry panels and seven strengthened panels were tested in diagonal tension/shear. Different reinforcement orientations were used including vertical, horizontal, and a combination of both. The effect of nonsymmetric reinforcement was also studied. The results of these tests are presented in this paper, and include the load-displacement behaviors, crack patterns, failure modes, and FRP strains. The results showed that the vertically aligned reinforcement was the most effective, with significant increases in strength and ductility observed. The dowel strength of the vertical reinforcement did not likely contribute significantly to the shear resistance of the masonry. Instead, it was likely that the vertical reinforcement acted in tension to restrain shear induced dilation and restrain sliding. In some panels cracking adjacent to the FRP strip, through the panel thickness was observed. This type of cracking reduced the bond between one side of the FRP strip and the masonry, and led to premature debonding. A comparison of the test results with the results of other tests from the literature is also presented in this paper.     

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.     

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.     

Experimental Evaluation of a Sacrificial Seismic Fuse Device for Masonry Infill Walls

Presented herein are the details and results of an experimental study conducted to evaluate the performance of a proposed infill wall fuse system. The purpose of this system, referred to as the seismic infill wall isolator subframe (SIWIS) system, is to prevent damage to columns or infill walls due to infill-frame interaction through a “sacrificial” component or a “structural fuse.” The SIWIS system conceptually consists of two vertical and one horizontal sandwiched light-gauge steel studs with SIWIS elements in the vertical members. The experimental study presented here involves the in-plane lateral load testing of a two-bay three-story steel frame in three forms of bare frame, infilled braced frame, and pinned frame equipped with the proposed SIWIS device. In addition, a brick wall in-plane strength test and a series of component tests on three different designs for fuse element were conducted. In the conducted tests, the suggested technique initially engages the infill walls in seismic resistance of the frame, but ultimately isolates them. It is concluded, thus, that the proposed fuse system has the potential for the development of an effective way to reduce earthquake damage in framed buildings with infill walls.     

Testing Block Probes for Wall Shear Stress Measurement in Water Flows

The authors developed and tested two types of sublayer pressure probe or blocks, to indirectly measure the average modulus and direction of the wall parallel component of the shear stress tensor, usually referred to as wall shear stress, or boundary shear, in water flows. The local shear stress has been investigated by means of a Preston tube for different Reynolds numbers, in a smooth rectangular section duct. The observed data have been used to calibrate the blocks. The blocks’ design is a direct outcome of the Dexter yaw meter, developed to function in an air flow. The observed pressure field associated with a given shear stress is compared to its theoretical counterpart, based on the assumption that the velocity profile satisfies a two-dimensional law of the wall, for smooth boundary.     

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.     

An Experimental Study on Turbulent Circular Wall Jets

The results of a laboratory investigation on the characteristics of a circular three-dimensional turbulent wall jet are presented. Measurements were performed up to 50 nozzle diameters using a combined Particle Image Velocimetry and Planar Laser Induced Fluorescence approach that captured simultaneously the planar velocity and concentration fields. Both the velocity and concentration profiles exhibited similarity in the streamwise and spanwise directions after sufficient distance from the nozzle. The existence of a secondary mean motion is shown to be responsible for the far greater lateral spread compared to the normal spread for both the momentum and scalar mixing. Using curve fitting, the mean properties of the three-dimensional wall jet are approximated. The consistency of the relationships is further examined based on mass conservation and momentum balance.     

Experimental Investigation of a Vortex-Flow Restrictor: Rain-Blocker Performance Tests

Flow restrictors, or rain blockers, are commonly used at inlets of storm-drain networks to limit the peak flow entering storm sewers. This reduces the likelihood of the sewer system becoming hydraulically overloaded, thus preventing sewer backups and residential flooding. The vortex-flow restrictor limits flow by forcing flow through a helicoidal chamber followed by sudden expansions and contractions that create high levels of turbulence. The high turbulence produced in a vortex-flow restrictor limits flow rates much more than a simple orifice, while maintaining a relatively large flow opening that can reduce the chances of clogging. Hydraulic tests were conducted with a vortex-flow restrictor (FR Type I) as well as a modified version in which the vortex chamber was removed (FR Type II), in which case the restrictor works a simple orifice plate. Discharge coefficients were calculated for the tested flow restrictor configurations and were compared to the case in which no flow restrictor was in place.     

Flow Details near River Groynes: Experimental Investigation

Experiments have been carried out in a fixed-bed flume for a schematized straight river reach with groynes on one side to study the dynamics of the flow near groynes. The flume had a geometrical scale of 1∶40, based on typical dimensions of the Dutch River Waal. Both emergent and submerged groynes were studied. The measurements demonstrate the differences in the nature of the turbulence between submerged and emerged groynes stages; and provide insight into the flow pattern in the vicinity of groynes, the shape and the extent of the mixing layer at different flow stages, and the dynamic behavior of the velocity along the mixing layer between the main channel and the groyne fields. A parameterization of the turbulence characteristics of the flow near groynes is presented. Large-scale velocity fluctuations are found in all test cases, with timescales that vary with the flow stage. The large-scale u and v velocity fluctuations are in phase in the center of the mixing layer and out of phase for the points on the boundaries of the mixing layer.     

Investigation of Seismic Behavior and Infill Wall Effects for Prefabricated Industrial Buildings in Turkey

Recently, Turkey has been hit by several moderate to large earthquakes that resulted in significant loss of life and property. The 1998 Adana and 1999 Marmara earthquakes caused severe damage not only in residential buildings but also in industrial buildings. Most of the industrial buildings in Turkey are constructed as prefabricated structures. Prefabricated structures are preferred because of their economic and rapid production. In the present study, the earthquake behavior and infill wall effects for single story hinged industrial prefabricated buildings were investigated. Nonlinear pushover, performance-based, time history, and fragility analyses were carried out for a sample prefabricated industrial building. Infill wall effect was investigated by adopting a diagonal strut model. The structural behavior and load-deformation relationship of prefabricated industrial buildings both with and without infilled walls were evaluated and compared. Results of the study show that masonry infill walls can affect the lateral load-carrying capacity and modify the earthquake response of prefabricated industrial buildings.     

Experimental Investigation of Flow Past a Square Cylinder at an Angle of Incidence

Flow past a square cylinder placed at an angle to the incoming flow is experimentally investigated using particle image velocimetry, hot wire anemometry, and flow visualization. The Reynolds number based on cylinder size and the average incoming velocity is set equal to 410. Data for four cylinder orientations (θ = 0, 22.5, 30, and 45°) and two aspect ratios [AR = 16 and 28] are reported. Results are presented in terms of drag coefficient, Strouhal number, time averaged velocity, stream traces, turbulence intensity, power spectra, and vorticity field. In addition, flow visualization images in the near wake of the cylinder are discussed. The shape and size of the recirculation bubble downstream of the cylinder are strong functions of orientation. A minimum in drag coefficient and maximum in Strouhal number is observed at a cylinder orientation of 22.5°. The v-velocity profile and time-average stream traces show that the wake and the separation process are asymmetric at orientations of 22.5 and 30°. The corresponding power spectra show additional peaks related to secondary vortical structures that arise from nonlinear interaction between the Karman vortices. The flow visualization images show the streamwise separation distance between the alternating vortices to be a function of cylinder orientation. Further, the flow approaches three dimensionality early, i.e., closer to the cylinder surface for the 22.5° orientation. The drag coefficient decreases with an increase in aspect ratio, while the Strouhal number is seen to increase with aspect ratio. The turbulence intensity is higher for the large aspect ratio cylinder and the maximum turbulence intensity appears at an earlier streamwise location. The overall dependence of drag coefficient and Strouhal number on orientation is preserved for the two aspect ratios studied.     

Experimental Investigation of Nonconventional Confinement for Concrete Using FRP

The present study investigates experimentally the behavior of concrete confined with fiber reinforced polymers (FRP) in the form of jackets which are applied according to a number of nonconventional techniques. First, the effectiveness of various jacketing configurations combined with anchors as a measure of increasing the strength and deformability of L-shaped columns is investigated. It is concluded that easy to install and low-cost anchors made of resin impregnated fibers properly placed at the reentrant corner of L-shaped columns enable excellent mobilization of confining stresses supplied by the FRP jackets. Next, a number of alternative confinement methods are investigated on concrete cylinders, aimed at quantifying the effectiveness of (1) unbonded jacketing, (2) spirally applied strips attached only at their ends, and (3) jacketing directly on concrete with mortar plastering. Although the study may be regarded as preliminary, it provides useful experimental support to a number of techniques which have the potential to open new horizons in the field of externally applied FRP for enhancing concrete confinement.     

Lateral Load Resistance Evaluation of Wood- and Steel-Stud Partition Shear Walls

This paper summarizes the findings of an experimental study to characterize the cyclic racking and monotonic loading performance of wood-stud and steel-stud wall specimens, which were sheathed on both faces with gypsum wall board (GWB). Some specimens were finished with joint compound at the GWB joints and over screw heads. The study provided data on monotonic and cyclic hysteresis load-displacement relationships. Based on the visual inspection of the specimens during the tests, several aspects of the failure modes were noted. Shear-load capacity and drift capacities were determined based on the envelope curves of the hysteresis cycles. A comparison of the envelope curves for steel-stud and wood-stud specimens provided insight as to the relative behaviors of the two wall system types, including capacity, measures of ductility, and energy dissipation. Finally, the study provided better understanding of the effects of finishing GWB joints on the shear capacity of the wall systems.     

Comparison of CFRP and Alternative Seismic Retrofitting Techniques for Bare and Infilled RC Frames

The opportunities provided by the use of modern repair schemes for the seismic retrofit of existing RC structures were assessed on a comparative experimental study of carbon fiber-reinforced polymer (CFRP) and more-conventional seismic retrofitting techniques for the repair of reinforced concrete members and masonry walls of bare and infilled RC frames, respectively, damaged because of cyclic loading. Four 1-story, one-bay, one-third-scale frame specimens are tested under cyclic horizontal loading up to a drift level of 4%—two bare frames with spirals or stirrups as shear reinforcement, respectively, and two infilled frames with weak infills and spirals or stirrups as shear reinforcement, respectively. The applied repair techniques are mainly based on the use of thin epoxy resin infused under pressure into the crack system of the damaged RC joint bodies or on the additional use of CFRP plates to the surfaces of the damaged structural RC members as external reinforcement and the use of a polymer modified cement mortar or two-sided diagonal CFRP fabrics for the damaged infill masonry walls. After repair, specimens were retested in the same way. Conclusions concerning the comparison of the effectiveness between conventional and CFRP seismic retrofitting applied techniques on the basis of maximum cycles load, loading stiffness, and hysteretic energy absorption capabilities of the tested specimens are drawn.     

Experimental Investigation of the Pressure Distribution beneath a Floating Ice Block

Discrete ice floes approaching an ice cover from upstream will contribute to the lengthening of the cover or will become entrained in the flow. Currently, ice process models rely on empirical relationships to predict the behavior of ice floes at the leading edge of an intact ice cover. Knowledge of the hydrodynamic forces acting on individual ice floes is an important component of any model attempting to predict ice-cover progression. Experimental studies were conducted in a recirculating flume in the T. Blench Hydraulics Laboratory at the University of Alberta to increase the knowledge of the physical behavior of ice floes in water and the hydrodynamic forces that act on them. A hollow Plexiglas acrylic ice block outfitted with pressure taps was constructed to facilitate measurements of the pressure distribution beneath an ice block. The dynamic pressure was measured under the block for various block thickness-to-depth ratios and flow velocities. The dynamic pressure was found to decrease for increasing block thickness-to-approach flow depth ratios and increasing flow rates. A block with a rounded leading edge was also tested, and it showed a significantly reduced leading-edge pressure effect. The rectangular ice block results were categorized into separate effects: a pressure reduction attributable to Venturi effects and a pressure reduction attributable to leading-edge effects. A predictive relationship was developed for the pressure distribution beneath a floating ice block and the subsequent submerging force and underturning moment.     

Experimental Investigation on Square High-Strength Concrete Short Columns Confined with AFRP Sheets

An experimental investigation on square high-strength concrete short columns confined with aramid fiber-reinforced polymer (AFRP) sheets is carried out in this study. Nine plain concrete specimens and 54 wrapped concrete specimens were tested under monotonic axial compressive loading. The specimens were grouped by three different grades of concrete strength. In each grade, some specimens were partially wrapped and others were fully wrapped, and the amount of wrapping AFRP sheets was varied also. Based on the experimental results, the regression formulas for strength and strain are obtained. The experimental results demonstrate that two types of axial stress-strain curves were observed depending on the form of AFRP wrapping, and the strength and ductility of the columns were increased when fully wrapped AFRP sheets, while only the strength was increased when partially wrapped AFRP sheets.     

Seismic Protection of a Building Complex Using Variable Friction Damper: Experimental Investigation

This study presents an experimental investigation of seismic control of a building complex using variable friction damper. The laboratory-scale building complex was composed of a 12-story building and a three-story podium structure coupled in different configurations. The laboratory-scale variable friction damper was tailor made with a piezoelectric actuator. The performance test of the piezoelectric actuator was carried out to identify its characteristics. The performance test was then conducted on the piezo-driven variable friction damper under either constant or varying voltage to identify its motion-independent characteristics. Based on the characterization results, a close-loop operating scheme was proposed together with two classes of semiactive controllers: local-feedback controller and global-feedback controller, for real-time manipulation of the damper. The building complex was finally tested in uncoupled, rigid-coupled, passive damper-coupled, and semiactive damper-coupled configurations. The control performance of variable friction damper for the building complex was examined and compared with other cases. The test results showed that semiactive coupling control was promising for reducing seismic responses of both buildings.