Date

2016

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Civil Engineering

First Adviser

Naito, Clay

Other advisers/committee members

Pakzad, Shamim; Sause, Richard; Quiel, Spencer; Schumacher, Thomas

Abstract

The design of structural systems is a complex process which encompasses many different aspects of structural engineering. The design process includes understanding the load demands placed on the system, designing and detailing the structural components to withstand the demands and the fabrication/construction of the final system design. The work presented in this dissertation covers a breath of topics within the field of structural engineering including: site assessment procedures for structures subjected to tsunami generated debris, the development of an innovative composite bridge system and shear connection and non-destructive evaluation of fully grouted post-tensioned bridge systems. Collectively, the original research contributions in each of three topics resulted in improvements to the overall design process of structural systems. The advancements to the design process presented in this dissertation include: assessment of demands on structural systems, developing new detailing of structural components, overall design changes to allow for improved inspection techniques and the development construction and fabrication methods for a prototype system.Currently, the United States has no codified guidelines in place for designing against the effects of tsunami events despite having a number of tsunami prone areas including: Alaska, California, Hawaii, Oregon and Washington. The lack of design guidance has left many coastal communities in the U.S. at risk. Recent tsunami events including Japan 2011, Chile 2010 and Indian Ocean 2004, motivated the engineering community to understand the effects of these events and to develop methods to design structural systems to withstand tsunami generated loads. This research effort was focused on developing site assessment procedures for structures subjected to tsunami generated debris impacts. A debris classification system was developed to group debris by the potential impact demand each item can generate. Four characteristics that contribute to the impact force demand for debris items where identified including debris: mass, stiffness, buoyancy and cumulative length. Based on these characteristics debris items are grouped into three categories, small, moderate of large debris. Small debris items will generate low level demands on the systems typically an impact force of 6000 lbs. or less large debris items will generate extreme levels of demand, typically an impact force of 1000 kips or greater and moderate debris is any debris item that generates an impact force that falls in-between. Large debris items such as shipping containers and shipping vessels can place extreme loads on structural systems resulting in collapse of the system if not properly designed. An impact hazard region was developed which provides design engineers with a probable region over which large debris items will disperse in a tsunami event. Knowing the location of the debris origin and the assumed flow direction of the event the impact hazard region can be constructed for any tsunami prone location. The development of the debris impact hazard region allows design engineers to determine, based on the location of a structure, if design against impact of large debris is necessary. The impact hazard region has been adopted by ASCE 7-16.The energy grade line (EGL) method, used to approximate water velocity and inundation height at a building site within an inundation region, has not yet been widely validated within the archival literature. Analytical results utilizing the EGL method were generated for a region of Hawaii and compared with results from a two-dimensional tsunami inundation simulation. Based on this comparison it was found that the EGL was under estimating the water velocity and inundation compared to the site-specific analysis. This under estimation was attributed to the discrepancy in runup elevation at the inundation limit provided by ASCE runup data and the corresponding elevation obtained for the same location using the available digital elevation model data. A modification to the EGL method to account for this discrepancy in elevation was proposed to improve the estimates of the EGL method, which extends the EGL transect past the inundation limit to an elevation on the DEM equal to the runup elevation provided by ASCE. Applying the modification to the energy grade line method results in more conservative approximations of water velocity and inundation height then the traditional energy grade line method as compared with the results of the site-specific analysis.Composite bridge systems have gained interest in the structural engineering community due to the ability for these sections to be cost effective alternatives to traditional steel or concrete systems. When properly designed, these systems take advantage of the ability for concrete to perform well under compressive stress and the ability of steel to resist the tensile stress. Composite systems can also allow for a more rapid construction time as a result of the ability for these sections to be prefabricated. The result of this research project is the development of a precast steel/concrete composite highway bridge system whose beam components are light-weight and easy to erect and fabricate. This research effort examines the shear transfer mechanism between the concrete slab and WT web and developed construction methods for the prototype system. A series of potential shear connector details were experimentally examined with push-off tests for the shear connection developed for the prototype system. A number of shear connector detailing parameters including the effect of: hole size, hole spacing, bar size and bar geometry were investigated. If was found that increasing the hole size and bar size increased the shear capacity of the connection. Increasing the hole spacing resulted in a decrease in capacity and bending the rebar as opposed to using straight bars increased the capacity. Based on the experimental testing the connector details utilized in the prototype system design was 1.5 inch holes with #6 bars through every hole, where the spacing of the holes is dependent on the shear demand along the length of the beam.Based on the experimental test data and destructive evaluation of the test specimens the failure mechanism for the connectors was determined attributed to two mechanisms. In the case where no reinforcement was placed through the connector the ultimate strength is attributed to shearing of the concrete dowels and in the case where rebar was placed through every connector hole the ultimate strength is attributed to initial yielding of the reinforcing bar. A design equation to approximate the capacity of the shear connection was developed based on the observed failure mechanisms and experimental test data.The prototype system shear details were designed based on the developed equation to approximate the shear capacity of the connection. The final design for the WT 20 x 74.5 system required 50 1.5 inch holes, with #6 bars in every hole in the half-span. Three different hole spacing was utilized in the half-span to meet the shear demands: 4 in., 6 in. and 11.25 in. spacing. Fabrication and construction methods were established for the newly developed prototype system, which were aimed at reducing fabrication cost and assuring critical dimensions of the system, such as embedment of the WT into the deck, are maintained for all precast components. Due to the fact that the WT section as well as the individually precast composite segments can be unstable at long lengths, a laterally torsional buckling analysis of the sections was performed. AISC design equations can directly be applied to the WT section; however, for the composite section design equations are not available so as part of this effort the available AISC equations were modified based on concrete limit states for construction loading and applied to the individual precast components.Post-tensioned concrete bridges represent a major component of the American bridge inventory and due to the benefits provided by this construction technique it is likely that many new post-tensioned concrete bridges will be built in the future to meet our infrastructure needs. However, recent cases in which corroded post-tensioning tendons were identified have caused industry wide concern and lead to a moratorium on post-tensioned constructions in some states. Post-tensioning systems are comprised of unique structural details including prestressing strand, ducts, anchorages, grout, and corrosion protection equipment. Current details for the construction of post-tensioning tendons do not facilitate the long term inspection of the various tendon components. As part of this research effort a state of the art review of available NDE techniques that can be applied to fully grouted post-tensioned systems was conducted. Currently available NDE methods were grouped into four different categories by monitoring capabilities: grout voids identification, strand corrosion detection, identification of tendon location and determining loss of prestress. Based on the state of the art reviews it was concluded that methods that can be directly integrated into future construction show the most promise for long term monitoring of post-tensioned tendons. A testing plan for two promising non-destructive testing methods, the electrically isolated tendon system and internal half-cell potential method, was developed. This testing plan has not yet been implemented, but outlines the design of a test specimen and testing procedures that can be utilized to verify the long term monitoring capabilities of the system as well as perform a sensitivity study on the level of damage which can be detected.

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