Ian N. Robertson

GRAVITY LOAD EFFECT ON SEISMIC BEHAVIOR OF INTERIOR SLAB-COLUMN CONNECTIONS

The effect of superimposed slab loading on the behavior of exterior slab-column connections was studied by testing 2-bay slab-column subassemblies. Each subassembly consisted of an interior and two exterior connections. Three identical slab-column subassemblies were subjected to the same cyclic lateral-displacement history while each supported a different superimposed slab load. The tests show that increased slab load substantially reduces the lateral drift capacity of the connections. A limiting shear stress is suggested to insure adequate drift capacity for exterior slab-connectiions. A rational method to calculate the moment capacity of exterior connections is developed. The test results are compared with present ACI 318-83 Building Code provisions and ACI Committee 352s recommendations for design of slab-column connections.

Cyclic Lateral Loading of Nonductile Slab-Column Connections

Flat slabs with discontinuous bottom reinforcement are susceptible to progressive collapse if punching shear failure occurs at a slab-column connection. Many such failures have occurred in past earthquakes, resulting in significant loss of life. The evaluation of older flat-slab buildings must include a realistic prediction of the response of the slab-column connections. Considerable research has been performed on connections with continuous slab reinforcement; however, there is a lack of data on the performance of slab-column connections with discontinuous reinforcement. The research presented in this paper involved the cyclic lateral loading of six slab-column connections with discontinuous slab reinforcement typical of flat-slab buildings built prior to 1970. Punching shear failure does not appear to occur earlier than in equivalent specimens with continuous reinforcement; however, the consequences are significantly more severe. Based on this and prior research studies, a model is proposed for estimating the lateral drift at which punching failure may occur.

TSUNAMI STRUCTURAL DESIGN PROVISIONS FOR A NEW UPDATE OF BUILDING CODES AND PERFORMANCE-BASED ENGINEERING

Since tsunami loading provisions were initially developed for Honolulu, Hawaii in the 1980s and subsequently utilized in other design guidelines for coastal construction, a comprehensive update of tsunami design provisions has not occurred. Furthermore, a national standard for engineering design for tsunami effects written in mandatory language does not exist. With the advent of the NSF George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) wave basin and wave flume facility at Oregon State University and the NSF/NEES research program, modern research using larger scale models has become available on which to base a new generation of tsunami design provisions. Devastating recent tsunamis in the Indian Ocean (2004), Samoa (2009), Chile (2010) and Japan (2011) indicate that explicit design procedures for risk mitigation of tsunamis is overdue. The recommended development of a new update of tsunami loading provisions will be discussed for prescriptive loading conditions for building codes and for the performance-based criteria for site-specific hazard analysis and design of essential facilities and other buildings.

Effect of Entrapped Air on Solitary Wave Forces on a Coastal Bridge Deck with Girders

AbstractRecent tsunami and hurricane-caused destruction, and the possibility of both tsunami inundation and storms of even greater magnitude and frequency making landfall in the future, has focused attention on the vulnerability of coastal structures, and bridges in particular. Findings from a series of experiments measuring forces on a 1:35 scale bridge model impacted by a solitary wave with varying percentages of air relief openings (AROs) between girders are presented here. A range of water depths, wave amplitudes, and elevations of the model above the still-water level (SWL) are considered. Results show significant reduction of vertical uplift forces when AROs are added to the bridge model, particularly when the girders are fully elevated above the SWL or only slightly submerged, but relatively little effect on horizontal forces in the direction of wave propagation is observed. Buoyancy calculations show added hydrostatic force does not alone contribute to uplift forces, but rather a combination of hy...

Analysis of Flat Slab Structures Subjected to CombinedLateral and Gravity Loads

The effective width and equivalent frame analysis methods are applied to a flat plate test specimen. The theoretical moment distribution and lateral drift show poor agreement with the test specimen results. A modified two-beam analytical model is proposed. This model allows for more appropriate modeling of the slab cracking in negative and positive bending regions. The modified model is able to reproduce both the slab moment distribution and lateral drift observed in the test specimen. Effective width factors, a, and slab cracking factors, β, are suggested for use in modeling of flat plates for lateral and gravity load analysis.

Vulnerability assessment of coastal bridges on Oahu impacted by storm surge and waves

Vulnerability assessment of four selected prototype coastal bridges on the island of Oahu, Hawaii, to the combination of storm surge and waves is presented. The maximum storm surge condition is estimated by considering an extensive series of simulated hurricanes making landfall on the island of Oahu, where the bridges are located. For the given extreme environmental conditions, wave loads on the deck of the selected bridges are calculated by use of several theoretical and computational approaches, including Euler’s equations (OpenFOAM), the Green–Naghdi nonlinear equations, linear long-wave approximation and existing simplified, design-type force equations. Multiple scenarios of the relative location of the bridge deck and the still-water level are studied to determine the maximum possible wave loads on the bridge decks. Vulnerability of the coastal bridges to storm wave loads is determined by comparing the capacity of the bridge to the wave-induced loads on the structure.

Soil and Rock Properties in a Young Volcanic Deposit on the Island of Hawaii

Deeply weathered lava flows of oceanic basalt reflect the mode and sequence of volcanic deposition, parent mineralogy, and postdepositional erosional and weathering processes. In turn, these are controlled by geology, geography, and climate. One particular site on the Island of Hawaii has been the focus of study to gain a better understanding of complex residual soil deposits, particularly in connection with a need to characterize seismic strong-motion propagation through decomposed surface soil and rock sequences. Materials at the site range from fully weathered volcanic soils, sometimes with unusual mineralogy and plasticity properties, to saprolite, weathered rock, vesicular basalt, and hard rock. Seismic surveys were conducted to investigate the distribution of these materials at the study site. Laboratory tests focused on saprolite and vesicular rock as two materials that are seldom reported on and that remain poorly characterized, at least with regard to conditions found in Hawaii.

Development of Performance Based Tsunami Engineering, PBTE

In 2005, the US National Science Foundation funded a project through the Network for Earthquake Engineering Simulation to develop Performance Based Tsunami Engineering, PBTE. The primary objective of this study is the development of design guidelines and computational tools that can be used by engineers to design coastal structures to resist tsunami loads. This involves improved inundation and scour modeling, as well as determination of structural loading time histories and loading expressions for use in structural design. This paper presents preliminary results for some of the laboratory experiments performed to determine tsunami bore loading on structural components. In particular, results are presented for the effects of multiple column arrangements that are typical for the ground floor layout of a multi-storey coastal building.

Ductile Fuse Connectors for Hybrid Masonry Systems

The National Science Foundation is funding hybrid masonry research to investigate the seismic strength, behavior, and performance of structural steel frames braced with hybrid masonry. One aspect of the research is a sub-study performed at the University of Hawaii at Manoa (UHM) to investigate the strength and behavior of steel connector plates that transfer story shears from the structural steel frame to the masonry panels. Results of this sub-study were then used in large-scale testing at the University of Illinois at Urbana-Champaign (UIUC). The primary goal of the study was to determine whether the connector plates can be developed as ductile fusible links for the overall system under seismic events. This paper presents the results of a series of experiments performed in the structures laboratory at UHM. Details of the experiments are summarized and sample results are presented that illustrate expected behavior of the connector plates, bolts and masonry for the large-scale experiments performed at UIUC. Some connectors were designed as link plates with sufficient strength to transfer full story shears to masonry panels without yielding, whereas other connectors were designed to behave as energy dissipating ductile fuses. These fuse plates will absorb most of the seismic deformation, thereby protecting the masonry and steel frame elements from damage. The fuses can then be replaced after the earthquake to restore the hybrid masonry system to its original condition.

Instrumentation Performance During Long-Term Bridge Monitoring

This paper reviews the performance of a variety of instruments installed in the North Halawa Valley Viaduct for a 10-year monitoring program. Over 200 electrical strain, displacement, temperature and load sensors were installed during construction of the long-span box-girder viaduct on the island of Oahu in 1994. These instruments have been monitored continuously since installation. Comparisons are presented where two types of sensor were used to monitor the same response. Each of the instrumentation systems is evaluated for its performance in monitoring short-term and long-term response. Advantages and disadvantages are presented for each type of sensor used in this project.