Liam Wotherspoon

Investigation on the Impact of Seasonally Frozen Soil on Seismic Response of Bridge Columns

This paper presents the development of numerical models that investigated the seismic response of a simple two span prototype bridge system during warm and frozen temperatures. Models from both temperature conditions were subjected to a range of seismic intensities to examine the effect of seasonal freezing on the response of the system. Stiffness characteristics were defined using cyclic models of a bridge pier that were previously developed and validated using results from an experimental program on identical full-scale column-foundation units, which were tested during the summer and winter months. Dynamic characteristics of the seismic models were defined using approaches found in the literature. Frozen conditions increased the maximum bending moment and shear force demands for all seismic intensities, with nonlinearity in the column/foundation reducing the difference between the peak responses at higher intensities. At the depth of maximum foundation shear for the frozen model, demand was three times ...

Spreading-Induced Damage to Short-Span Bridges in Christchurch, New Zealand

This paper discusses the performance of road bridges during the 2010–2011 Canterbury earthquakes and focuses on the response of bridges in liquefying soils undergoing lateral spreading. A characteristic spreading-induced mechanism for short-span bridges with rigid superstructures is presented and explored using four well-documented case studies. A series of pseudo-static analyses are then used to investigate the observed response of the bridges and their pile foundations in particular. Deformations and damage to the piles are evaluated and correlated with the spreading displacements, and key factors controlling the pile response and the development of the spreading-induced damage mechanism are identified.

In-Plane Strengthening of Unreinforced Concrete Masonry Wallettes Using ECC Shotcrete

AbstractAn experimental program was conducted to investigate the viability of using engineered cementitious composite (ECC) shotcrete as in-plane shear reinforcement for concrete masonry wallettes. Twenty-six mortared or dry-stacked ungrouted and unreinforced concrete masonry wallettes were strengthened through the application of an ECC shotcrete mix, applied either by spraying with a shotcrete machine or by hand trowelling. To determine the effect of applicator experience, ECC was applied by both a professional plasterer and amateur plasterers, with and without supervision. The in-plane shear strength of the strengthened wallettes increased between 340 and 3,471%, depending on the ECC application method. The variability of the strength increase was smaller for wallettes that had mortared joints and an ECC overlay trowelled by a professional plasterer. A set of design equations was also developed to determine the shear strength of a strengthened wallette. The design displacement ductility can be conservat...

Soil profile characterization of Christchurch strong motion stations

This paper presents an overview of the soil profile characteristics at a number of strong motion station (SMS) sites in Christchurch and its surrounds. An extensive database of ground motion records has been captured by the SMS network in the Canterbury region. However in order to comprehensively understand the ground motions recorded at these sites and to be able to relate these motions to other locations, a detailed understanding of the geotechnical profile at each SMS is required. The original NZS1170.5 (SNZ 2004) site subsoil classifications for each SMS site based on regional geological information and well logs located at varying distances from the site. Given the variability of Christchurch soils, more detailed investigations are required in close vicinity to each SMS. In this regard, CPT, SPT and borehole data, and shear wave velocity (Vs) profiles in close vicinity to the SMS are currently being used to develop representative soil profiles at each site. Site subsoil classifications based on Vs measurements performed by the authors do not always agree with the original classifications, often indicating that a softer site class is appropriate. However, SPT N values often indicate a stiffer site class than the Vs data, in some cases also disagreeing with prior assumed classifications. Hence, the recent site investigation data presented herein highlights the importance of having detailed site-specific information at SMS locations in order to properly classify them. Furthermore, additional studies are required to harmonize site classification based on SPT N and Vs.

Dynamic Field Testing of a Three-Span Precast-Concrete Bridge

AbstractThere has been little full-scale physical experimentation to support the findings of numerous computational studies regarding the contribution of various substructure components to overall bridge-foundation system behavior. In response to this lack of experimental data, a field testing program was undertaken to investigate the in situ dynamic characteristics of a 27-m-long, three-span, precast-concrete bridge. Forced vibration testing and system identification were used to characterize the dominant modal behavior of the bridge-foundation system in each loading direction, leading to identification of the likely force-transfer mechanisms between the structure and the substructure components. It was determined that both the transverse and longitudinal responses of the bridge were dominated by the abutment stiffness, with the passive resistance of the buried settlement slab contributing significantly to the transverse response and the backfill passive resistance dominating the longitudinal response.

Geotechnical aspects of the Mw6.2 2011 Christchurch New Zealand Earthquake

The 22 February 2011, Mw6.2 Christchurch earthquake is the most costly earthquake to affect New Zealand, causing an estimated 181 fatalities and severely damaging thousands of residential and commercial buildings. This paper presents a summary of some of the observations made by the NSF-sponsored GEER Team regarding the geotechnical/geologic aspects of this earthquake. The Team focused on documenting the occurrence and severity of liquefaction and lateral spreading, performance of building and bridge foundations, buried pipelines and levees, and significant rockfalls and landslides. Liquefaction was pervasive and caused extensive damage to residential properties, water and wastewater networks, high-rise buildings, and bridges. Entire neighborhoods subsided, resulting in flooding that caused further damage. Additionally, liquefaction and lateral spreading resulted in damage to bridges and to stretches of levees along the Waimakariri and Kaiapoi Rivers. Rockfalls and landslides in the Port Hills damaged several homes and caused several fatalities.

Seismic Performance of Improved Ground Sites during the 2010-2011 Canterbury Earthquake Sequence

The city of Christchurch and the surrounding region on the South Island of New Zealand are underlain by large areas of recent alluvial sediments and fills that are highly susceptible to liquefaction and seismic ground failure. Thus, the widespread liquefaction that occurred following the successive large-scale earth-quakes, with moment magnitudes (MW) ranging from 6.0 to 7.1 that struck the Canterbury region in 2010–2011 was expected. Prior to the series of earthquakes, soil improvement had been used at several sites to mitigate the anticipated damage. This paper reviews the performance of improved sites during the Canterbury earthquake sequence. The existing soil conditions at each site and the design of the ground improvement are discussed, together with descriptions of the post-earthquake damage observed. Moreover, liquefaction assessment within and surrounding a selection of the ground improvement zones is presented.

Development of Deep Shear Wave Velocity Profiles with Estimates of Uncertainty in the Complex Inter-Bedded Geology of Christchurch, New Zealand

Deep (+500-m) shear wave velocity (V S ) profiles were developed at 14 sites throughout Christchurch, New Zealand, using a combination of active-and passive-source surface wave testing. The geology of Christchurch is complex and presents several challenges for surface wave testing. Specifically, the complex interlayering of relatively stiff gravels with soft sands, silts, and clays makes (1) the interpretation of experimental dispersion data ambiguous and (2) complicates the determination of appropriate inversion-layering parameterizations. In order to address the first issue, dispersion data uncertainty was quantified and several mode interpretations were considered during inversion. To address the second issue, 155 geotechnical boreholes and 199 geologic well logs in the vicinity of the test sites were used to guide the choice of layering parameterizations such that geologically realistic V S profiles were obtained via surface wave inversion. At each site, a suite of 1,000 V S profiles representing the combined effects of epistemic uncertainty and apparent aleatory variability in V S was obtained. These V S profiles are available on the DesignSafe-CI web site (https://doi.org/10.17603/DS21D4D) and are intended to aid in future seismic site response analyses.

Mitigation Effect of Vertical Walls on a Wharf Model Subjected to Tsunami Bores

An experimental study was carried out to investigate the mitigation effect of vertical walls on a wharf model subjected to tsunami bores. Dam-break waves were generated in a flume to simulate tsunami bore propagation, the bore characteristics were observed, and the tsunami pressures on vertical walls and a wharf model were measured. Results indicate different characteristics for bores traveling on wet-bed and dry-bed. The tsunami bore impact on a vertical wall was shown to exhibit four stages, and the time-history of the pressure exhibits three phases accordingly. Based on the law of conservation of energy, an equation for estimating the pressure exerted on the mid-point of the wall was proposed with coefficient of 1.8–2.4, and found to be suitable in this experimental range. Based on experimental data, an equation of the mitigation effect of vertical walls on tsunami was proposed as a function of the inundation depth, the wall height and the deck height. The predicted values from the equation are generally within ±20% of the measured values.

Durability Properties of Sprayed Engineered Cementitious Composite

Engineered cementitious composite (ECC) shotcrete is a sprayable cement composite reinforced with synthetic fibers that exhibits a strain-hardening characteristic under tension. The ductile behavior of ECC makes it an ideal repair material for concrete structures as tensile strains from expansion of the original concrete structure can be accommodated. The aim of the reported research was to develop an ECC mixture design having superior durability properties while exhibiting a strain-hardening characteristic. Six mixture designs of ECC and a 5800 psi (40 MPa) cast-inplace concrete were tested using four test methods to determine their chloride resistance. Results from bulk diffusion testing showed that the most effective ECC mixture design, which incorporated a metallic soap additive, showed a 90% reduction in the chloride diffusion coefficient when compared with a 5800 psi (40 MPa) cast-in-place concrete. The alternating current (AC) resistivity, void, and sorptivity tests conducted did not show a strong correlation to the bulk diffusion test.