Now showing 1 - 10 of 124
  • Publication
    Expansive fracture agent behaviour for concrete cracking
    (Institution of Civil Engineers/Thomas Telford Publishing, 2010-06) ; ; ; ; ;
    Increasing concerns regarding litigation and terrorism provide a strong dual motivation to decrease high explosives usage in the construction industry. This paper provides parameter considerations and initial guidelines for the application of expansive fracture agents, typically used for concrete and soft rock removal. This approach may be especially appropriate near environmentally and historically sensitive sites. Thirty-three unreinforced blocks (approximately a cubic meter each) of varying strengths composed of sand, cement, and flyash were tested under various temperature environments, with differing expansive agents, confinement levels, and post-cracking treatments. Cracking characteristics such as crack initiation and crack expansion were analyzed. Although the performance of expansive cement was dependent upon a highly complex set of variable interactions, higher ambient temperatures, higher agent mixture temperatures, and chemical configuration designed for colder temperatures decreased the time to first crack and hastened the extent of cracking. Conversely, higher strength material required more time to first crack, as well as an extended time to achieve a 25.4 mm wide crack. Manual interference with the normal material volume expansion slowed the cracking process but did not truncate it, while the manufacturer’s recommendation to introduce water post-cracking actually reduced and slowed the extent of cracking.
      1749Scopus© Citations 51
  • Publication
    Soil nailing in glacial till : a design guide evaluation based on Irish and American field sites
    (American Society of Civil Engineers, 2010) ; ;
    The French in-situ earth retaining system soil nailing began in 1970 and benefited greatly from that government’s investment in the 1986 study ‘Clouterre’. As such, French geology strongly influenced both practice and expectations world wide over the past four decades. Yet, recent studies in glacial till, a non-French soil type, have shown significant strength under-estimation using conventionally accepted design approaches. The paper reconsiders skin friction expectations for soil nail installations in glacial till. Installation at three glacial till sites (one American and two Irish) are examined in detail. Traditional British, French, and American de-sign methods and parameters are applied. Conventional methods under-predicted capacity by more than 50%, thereby raising serious questions as to the appropriateness of such design guidelines in glacial tills. New correlations based on pile installation design are proposed.
      1611Scopus© Citations 1
  • Publication
    Performance expectations of early 20th century urban American building foundations
    (American Society of Civil Engineering (ASCE), 2008-03)
    Foundation reuse is a tricky business at the best of times. For structures predating the mid-20th century, the challenge is exacerbated by the presence of a variety of foundation types, techniques, and materials no longer in current usage, such as lime based mortar. Accordingly, the modern engineer is presented with the difficulty of making decisions about assessment and intervention strategies for construction systems, geometries, and methods for which there is no applicable current building code or easily accessible textbook. As foundation reuse, particulary of early 20th century urban buildings, gains in popularity, accessing such information will only gain in criticality. This paper was designed to help amalgamate such information and provide upper limits regarding perfomance expectations of such foundations based on early 1900s’ building codes, practices, and testing data, with a typical upperbound of 10MPa in lime.
      1013Scopus© Citations 3
  • Publication
    Fostering development of women faculty in geotechnical engineering
    (American Society of Civil Engineering (ASCE), 2007-02) ; ;
    A one-day workshop was convened to address obstacles to success of American women faculty in Geotechnical Engineering. The workshop, sponsored by the National Science Foundation (NSF), was held in October 2003, in conjunction with another workshop for the United States Universities Council on Geotechnical Education and Research(USUCGER). At that time, the 17 participants represented 40% of all tenure-track women faculty in Geotechnical Engineering at American universities. The workshop provided an opportunity to discuss academic career issues, including diversity, research, teaching and service. Concerns voiced by the participants spanned all of these topics. The leading need that emerged was for childcare during professional activities away from home. For most major concerns, specific action items resulted, and these are presented. The NSF, USUCGER, professional organizations such as the American Society of Civil Engineers, university governance, and the women faculty themselves were seen as potential catalysts for problem-solving. Some concerns such as service loads and recognition for diversity-based contributions still defied the envisioning of specific action items.
      987Scopus© Citations 3
  • Publication
    Predicting reinforced concrete frame response to excavation induced settlement
    (American Society of Civil Engineering (ASCE), 2009-11) ; ; ;
    In many tunneling and excavation projects, free-field vertical ground movements have been used to predict subsidence and empirical limits have been employed to evaluate risk. Validity of such approaches given the reality of two-dimensional ground movements and the influence of adjacent applied loads has been largely unknown. This paper employed analytical and large-scale experimental efforts to quantify these issues, in the case of a reinforced concrete frame structure adjacent to an excavation. Nearly half of all soil and building movements occurred prior to installation of the first tie-back, even when conservative practices were applied. Free-field data generated a trough half the size of that recorded near the building frames. Empirically based relative gradient limits generally matched the extent and distribution of the damage. Application of various structural limits also generally reflected global experimental response but did not fully identify local damage distribution. Fully free-field data or failure to include accurate two-dimensional soil displacements under-predicted building response by as much as 50% for low-rise concrete frames without grade beams.
      2567Scopus© Citations 36
  • Publication
    Experimental investigation of grouted helical piers for use in foundation rehabilitation
    Building rehabilitation is critical for numerous older urban areas, many of which have inadequate foundations to support new demands. Consequently, development of practical methods to strengthen existing foundations is crucial. In engineering practice, both subsurface grouting and helical piers have been widely used to address these issues by strengthening the foundation. If the solid shaft of a typical helical pier is replaced by a hollow shaft, then helical piers provide the ability to deliver grout. It is hypothesized that these grouted helical pier systems (GHPS) could address foundation strengthening needs. However, there is limited test data available to understand the mechanisms of load transfer and the potential load enhancement they provide. In this paper, grouting and pier placement tools were developed and tested on the large geotechnical centrifuge at the University of California, Davis. Experimental methods and procedures developed are presented, and observations regarding the formation of grout bulbs under different conditions are analyzed. Physical observation of the test specimens indicates that average grout bulb diameters of 0.6-1.9 times the helix diameter (Dh) are attainable. For similar grout mixes, 20-50% larger grout bulbs can be attained by adding just a modest amount of injection pressure.
  • Publication
    Reduction of lateral loads in abutments using ground anchors
    (Thomas Telford Ltd., 2013-11-01) ; ;
    In bridge design, economically addressing large, lateral earth pressures on bridge abutments is a major challenge. Traditional approaches employ enlargement of the abutment components to resist these pressures. This approach results in higher construction costs. As an alternative, a formal approach using ground anchors to resist lateral soil pressure on bridge abutments is proposed herein. The ground anchors are designed to minimise lateral forces at the pile cap base. Design examples for high stem abutments (heights 6–8 m) are conducted for a simple 33 m long concrete bridge span, with two to three traffic lanes. The abutments are supported by driven, reinforced concrete piles. As lateral forces at the pile cap are significantly reduced, only one row of piles is needed. When compared with common abutment design, the proposed approach halved the number of piles required and decreased the required abutment volume by 37%.
      1469Scopus© Citations 2
  • Publication
    Octree-based, automatic building façade generation from LiDAR data
    This paper introduces a new, octree-based algorithm to assist in the automated conversion of laser scanning point cloud data into solid models appropriate for computational analysis. The focus of the work is for typical, urban, vernacular structures to assist in better damage prediction prior to tunnelling. The proposed FaçadeVoxel algorithm automatically detects boundaries of building façades and their openings. Next, it checks and automatically fills unintentional occlusions. The proposed method produced robust and efficient reconstructions of building models from various data densities. When compared to measured drawings, the reconstructed building models were in good agreement, with only 1% relative errors in overall dimensions and 3% errors in openings. In addition, the proposed algorithm was significantly faster than other automatic approaches without compromising accuracy.
      842Scopus© Citations 39
  • Publication
    Visualisation of urban airborne laser scanning data with occlusion images
    Airborne Laser Scanning (ALS) was introduced to provide rapid, high resolution scans of landforms for computational processing. More recently, ALS has been adapted for scanning urban areas. The greater complexity of urban scenes necessitates the development of novel methods to exploit urban ALS to best advantage. This paper presents occlusion images: a novel technique that exploits the geometric complexity of the urban environment to improve visualisation of small details for better feature recognition. The algorithm is based on an inversion of traditional occlusion techniques.
      367Scopus© Citations 13
  • Publication
    Theoretical solutions for strength-scaled unreinforced masonry for scaled soil-structure experimentation
    Reduced-scale masonry testing offers advantages of lower costs and shorter schedules compared to full-scale testing, but achieving results reflective of full-scale behavior requires development and fulfilment of appropriate scaling relationships. In many model-scale experiments, geometric scaling occurs but kinematic and/or dynamic similitude is not fully satisfied. This paper describes the theoretical basis and evolution of the equations necessary to achieve kinematic similitude for soil-structure testing at one-gravity for unreinforced masonry. Critical considerations relate to preventing the soil from being overloaded. By adopting a standard linear relationship of increased soil stiffness with depth, the controlling principle becomes the application of restricted, scaled loads throughout the entirety of the structure-soil system. As such, material strength and stiffness must be scaled accordingly to respond appropriately under the reduced stress. An example is provided for an adjacent excavation experiment with related empirical verification and computational quantification.
      1501Scopus© Citations 4