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A numerical modeling study was carried out to investigate the dynamic behavior and lateral earth pressures on box-shaped culverts buried in dry cohesionless soils. Two dimensional plane strain finite difference models of 4m-high prototype box culverts having different wall flexibilities were analyzed using FLAC-2D Finite Difference Code. Within the analyses, uniaxial input motions composed of harmonic excitations with amplitudes of 0.25 g and 0.40 g and frequencies of 2 to 15 Hz were applied to the numerical models. Box culvert sections with different wall thicknesses were analyzed to investigate the effect of relative flexibility on the dynamic response. Shear strains, horizontal accelerations, wall deformations, and lateral dynamic earth pressures at various points on the culvert were monitored. Racking deformations were calculated from displacement data obtained from the analyses. Results of the numerical analyses were validated with those of the centrifuge tests performed under 40-g centrifugal acceleration. Racking deformations of the analyzed culvert models are in good agreement with the test data. Racking curves for culverts having different flexibilities were estimated based on numerical modeling results. Good agreement exists between the actual data and those predicted with the finite difference method. Dynamic lateral pressures acting on the side walls increase as the wall flexibility ratio decreases. For the range of excitation characteristics, dynamic force on the sidewalls of the box culvert may reach up to 2.8 times the at-rest lateral stress for the stiff prototype.

Renewable energy from Photovoltaic (PV) Systems is poised to reach the major milestone of grid parity in the coming years due to substantial decreases in the cost of silicon based PV technologies. One of the remaining hurdles to overcome in order to achieve grid parity is the Balance of System (BoS) cost which includes all of the costs other than the PV modules and electrical inverters. This paper presents a novel approach to the problem of racking and mounting for utility scale PV power plants and urban canopy applications with a new racking system design and installation process model. The goal of this design is to provide the most cost effective racking system for utility scale PV arrays. This system, called the Quad Pod, is predicated on the principles of pre-assembly to minimize labor cost and ultra efficient long span truss design to minimize material cost. Additionally, both approaches yield significant improvements in installation time and worker safety and comfort.

Air, water, and vapor barriers, collectively referred to as weather resistive barriers (WRB), are an essential component of the modern building envelope system. If water passes through the WRB to the interior of the wall assembly, a moist environment is created around framing members and interior drywall, leading to decay and mold growth. Therefore, in order to protect against the adverse structural and health effects associated with moisture entrapment in the wall assembly, the WRB must be protected against tear and puncture, maintaining a proper air and waterproofing layer. One concern that has arisen amongst engineers is the capacity of the WRB to resist tearing when the lightframe wall assembly, including sheathing, is subjected to seismic induced racking displacements. The objective of this paper is to evaluate the serviceability and ultimate performance of the WRBs, and characterize the potential failure mechanisms based on available literature and test results.

Full-scale “unitized”, four-sided structural sealant glazing (4SSG) curtain wall system mockups featuring a re-entrant corner were subjected to cyclic racking displacements in accordance with the American Architectural Manufacturers Association AAMA 501.6 protocol to determine serviceability and ultimate behavior responses. Glass fallout, sealant adhesive or cohesive failure, and glass cracking were identified as limit states and corresponding drift levels were determined. This paper describes the details of the techniques developed and used for analysis and shows example applications of the method to mockups with racking test results available. The video analysis measured the changes in distances between glass and frame, which was then used to calculate an effective shear strain of the structural silicone by a linear and quadratic method. An effective shear strain of 173% and 130% was calculated from a linear method and a quadratic method for a structural silicone when failure initiated. Test data from the manufacturer indicates the ultimate shear strain of the structural silicone occurs around 200%.

Full-scale, “unitized”, four-sided structural sealant glazing (4SSG) curtain wall system mockups featuring a re-entrant corner were subjected to cyclic racking displacements in accordance with the American Architectural Manufacturers Association AAMA 501.6 protocol to determine serviceability and ultimate behavior responses. Sealant cohesive failure and glass cracking were identified as limit states and corresponding drift levels were determined. The geometry of the mockup was used to develop equations that predicted the displacements of the glass, relative to the frame, based on the independent variable of inter-story drift. The displacements from those equations were then related to the effective shear strain of the structural silicone and the drift capacity of the system. This paper describes the concepts and results of the kinematic equations developed.

The "Big House" is the main administration building at Summit Station, Greenland. It is the center of camp life and supports the overall station operation, as well as providing common areas for dining, washing, and leisure for camp attendees and staff. Constructed in 1989 on a permanent snowfield at the apex of the Greenland Ice Sheet, the building is elevated above the snow surface on steel support columns to reduce the adverse effects of drifting due to accumulating and blowing snow. The annual rate of snowfall is typically 70 cm. Periodically, the building is lifted to maintain clearance above the snow grade. Absent lifting, the structure becomes completely drifted in. The Big House has been lifted on four occasions for a combined total height of 15 m. The lifting process can damage buildings through racking. An infrared survey was conducted to identify existing deficiencies in the building envelope that may either diminish the energy efficiency or compromise the structural performance, reducing the building's service life. Even located in such an extreme climate, this assessment found that the Big House is performing quite well after 20 years of service. The most significant issue was heat loss in localized areas through the building envelope. No major structural issues were observed.

Two full-scale precast concrete cladding panels were tested in 2011 on a full-scale five-story steel fame building at the E~Defense shake table facility in Japan. The panels were designed according to common U.S. practice. Two issues evaluated were: 1) the effect of acceleration on the cladding panel, and 2) the effectiveness of the current slotted-bolt sliding connection to allow for inter-story earthquake motion. The cladding tests represented one type of standard US cladding facade design where cladding is designed to accommodate inter-story drift though racking of individual panels. Panels were cast in Japan but steel connections were designed and fabricated in the US to accurately simulate the behavior of American cladding construction. A 50 mm vertical seismic joint was installed between the two panels. Two full-height column cover panels were tested, a return cover 3D shape, and a flat panel. Instrumentation measured the acceleration of the panels and the movement of the slotted connections. Findings include the ability of slotted connections to slide while being accelerated in a full scale 3D seismic motion and development of fragility curves relating damage to panel and/or floor acceleration.

Cathedral Hill Hospital (the California Pacific Medical Center) is a 15-story building to be constructed in Downtown San Francisco. The curtain wall system for this building is primarily of unitized design employing a four-sided structural sealant glazing (SSG) system. To ensure satisfactory seismic performance of the curtain wall system for this project, dynamic racking tests were carried out according to AAMA 501.6 procedure on curtain wall mockups constructed with vertical and horizontal mullions that had section properties similar to the ones that will ultimately be used on the building. Although the curtain wall system designed for this building is unitized, the preliminary tests reported in this paper were carried out on mockups that were constructed as stick-built. The objective of the preliminary tests was to evaluate the performance of structural sealants as well as the glass when the mockup is racked in a worst case scenario. The building and curtain wall design are explained and the results of racking tests presented.

The potential seismic performance of three storefront framing systems was evaluated. Racking tests were performed on the Oldcastle BuildingEnvelope TM FG3000, Series 3000 Thermal MultiPlane (3000-TMP), and FG-2000 storefront systems. Planar mockups and mockups with a reentrant corner detail were tested for each storefront system. Testing followed a modified AAMA 501.6 dynamic racking protocol to allow detailed observations of damage progression in the mockups. Mockup design, test setup, and loading protocol details along with test results and observations from the racking tests are presented.

Results of cyclic racking tests on EN-WALL 7250 unitized curtain wall system mockups are presented. Mockups had overall dimensions of 180 in. wide by 156 in. high and were comprised of nine glass panels adhered to aluminum framing with 3M™ VHB™ structural glazing tape structural seals and structural sealant weatherseals. Racking tests followed the AAMA 501.6 protocol to characterize the performance of the system. Tests were carried out in a step-wise manner in order to stop the test after each drift increment to inspect the mockup for any damage. A complete description of the unitized system design is presented along with test observations

Beginning in early 2006, the APA Research Center expanded to include the capability of testing full-scale three-dimensional houses. This paper summarizes results of wall bracing racking tests from a full-scale 25 x 37.5 x 9-ft-tall three-dimensional wood frame house. Monotonic wall racking loads were applied at the corner of the structure in line with a single wall (the 37.5-ft-long wall). The concept of the setup was to investigate the wall behavior as part of a three-dimensional structure i.e. walls and roof are built around it. The roof diaphragm was flat. No finishes (i.e. gypsum, siding, roofing, etc) were installed and the walls were essentially bare with the exception of the applied bracing panels. A total of 23 different tests were conducted. Wall racking was generally limited to 1.5 inches in displacement to minimize damage and repair between tests. Repair was made after each test and the 23rd tests was a repeat of the 1st to compare results after repeated testing of some of the same framing components. The focus of these tests was primarily on the International Residential Code, IRC, wood structural panel type wall bracing. A number of variables were studied, including: 1 Hold-down devices in building corners, 2 Return corners, both 2 feet and 4 feet, 3 Panel placement at corners or away from corners, 4 Single diagonal 1 x 4 bracing, 5 Isolated wood structural panel bracing, 6 Continuous wood structural panel bracing, 7 Continuous wood structural panel bracing cut around openings, 8 Walls braced only by 6:1 aspect ratio portal frames, 9 Wall braced with 50 percent 6:1 aspect ratio portal frames mixed with other continuous wood structural panel bracing. This paper is a summary that discusses the global response of the structure to the applied loads. For more detailed information, including a detailed analysis of local wall responses, please refer to Martin et al.

Damping is dependent on many variables and complex mechanisms that are not yet fully quantifiable in the design stage. This has led to generic assignments of viscous damping usually based on material type and at best based on height with reference to existing databases. This study will employ recent full-scale observations to demonstrate the role of the structural system’s dominant deformation mechanism frame racking vs. cantilever action – in energy dissipation capability. Specifically, it is shown that frame racking and other shear deformations dissipate more energy than the axial shortening associated with cantilever action. As such, the ratio of frame racking to cantilever action may offer a more robust and intuitive parameter better suited for use in predictive viscous damping models. This study serves as the first step in the development of such models, with a specific focus on serviceability design.

This paper summarizes the findings of a pilot study to determine whether the type of drywall joint compound will influence the shear strength of wood-frame stud walls sheathed with drywall. In this study, five 8 ft x 8 ft specimens were tested under in-plane cyclic racking loading following CUREE loading protocol for light-frame wall systems. Three specimens were finished using non-cement based joint compound and the other two using cement based joint compound. Based on the limited number of specimens tested, the results show that the use of cement based joint compound on drywall joints as in the specimens tested will result in higher wall shear capacity compared to similar specimens finished with conventional non-cement based joint compound. The failure modes for the specimens finished with the two different types of compound were different. The result of the study is particularly important for high seismic regions where interior stud walls in residential construction effectively take part in seismic resistance even though wood shear walls are normally used on exterior walls.

This paper presents a brief summary of seismic analyses for Caldecott Tunnel Improvement Project. It includes seismic hazard analysis, wave scattering analyses to evaluate soil structure interaction (SSI) for the proposed 4 th bore, and development of seismic coefficient for slope stability design. Probabilistic Seismic Hazard Analysis (PSHA) was used to establish the rock motion criteria; 1,500-year and 300-year return periods were adopted for the Safety Evaluation Earthquake (SEE) and Functional Evaluation Earthquake (FEE), respectively. The wave scattering analyses were performed using the spectrum-compatible time histories to account for localized geologic features including site specific topography and soil properties specific to the current project. The analyses enable evaluation of the degree of ground distortion that contributes to racking and ovaling of the tunnel liner. Seismic coefficients for several critical slopes near portals were also derived considering the concept of wave propagation within the slope mass.

The Bay Tunnel is a major water supply facility to be constructed between the San Andreas Fault and the Hayward Fault in the San Francisco Bay Area. The design earthquake for the Bay Tunnel has a return period of 1,000 years and a horizontal peak ground acceleration of approximately 0.6g. A full dynamic analysis of the Bay Tunnel, considering the soil-structure interactions, was performed to evaluate the performance of the tunnel final lining system during the design earthquake. This paper discusses the methods employed to perform the dynamic analysis and the results obtained. A brief comparison of the results from the dynamic analysis with those from the closed-form solutions and numerical racking analysis is also presented.

A research project was undertaken recently at Penn State University to study the simulated seismic performance of “Structural Sealant Glazing” (SSG) used to adhere glass panels to common curtain wall framing systems. In the most common type of SSG curtain wall construction, referred to as “two-side” SSG, two glass panel edges (typically opposing vertical edges) are adhered to the support framing using structural sealant, while the other glass panel edges are mechanically fastened to the support framing. In this study, full-scale two-side SSG curtain wall mock-ups consisting of three, side-byside glass panels were subjected to cyclic racking displacements to characterize their performance and to identify sealant and glass component failure modes under serviceability and ultimate racking displacement conditions. Attempts were also made to develop kinematic-based models to predict failure states (e.g., structural sealant failure) of the SSG curtain walls. This paper discusses the details of the predictive model and its evaluation on the basis of comparisons with mock-up test data. The model developed appears to give good estimates of the observed sealant failure drift. Conclusions and recommendations regarding appropriateness and limitations of the predictive model are provided.

This paper presents the technical approach and the results of site response and seismic soil-structure interaction (SSI) analyses performed to develop free-field and SSI racking deformation that the reinforced concrete box structure subway will experience during the design seismic event. The study compared results computed from different computer programs (SHAKE, FLUSH, and FLAC) using equivalent linear and nonlinear soil models. In addition, the effects of soil stratigraphy and the construction methods are evaluated and presented in this paper. Results of the analyses were compiled as racking curves to be used for final design of the reinforced concrete box structure.

Systems of ground anchors are increasingly used to support steep excavation slopes and stabilize landslides. These ground anchor systems are comprised of a pattern of post-tensioned tieback anchors and multiple, isolated anchor pads or beams; they are less steep than tieback walls and do not have a continuous face, or a structure that penetrates the potential sliding surface. This paper addresses systems that contain up to 200 anchors, with individual capacities of up to 2000 kN, that have been installed in geologic settings ranging from shale to crystalline bedrock, and the associated soils. Observations are presented from the alternatives selection process, the investigation, design, and construction phases, and monitored performance of recent highway projects in the Western United States. Specific design issues include analysis for anchor location, size, and length, bearing pad capacity and racking during tensioning and testing, desirable lock-off load, and corrosion protection. Specific construction issues include construction sequencing, allowable tolerances, and coordination with other items of work.

The Building Envelope Research Laboratory (BERL) in the Architectural Engineering Department at the Pennsylvania State University has devised and developed the concept of using architectural glass panels with modified corner geometries to improve their resistance to damage during earthquakes. The primary aspects of the invention are the removal of material at glass panel corners (e.g., by rounding the glass corners) and subsequent finishing of the glass edges in the modified corner regions to minimize protrusions and edge surface roughness. The invention is low in incremental cost and is applicable to a wide variety of architectural glass types and wall system types. Appropriately constructed rounded corner glass panels were found to increase significantly the serviceability (i.e., the dynamic racking displacement magnitude that can be accommodated before glass cracking occurs) and, to a lesser extent, the glass fallout resistance of architectural glass panels used in building wall systems. The effects of corner radii and glass edge finish conditions on the glass cracking and glass fallout resistances of rounded corner glass panels subjected to dynamic racking displacements are summarized.