Browsing by Subject "concrete"

Now showing 1 - 4 of 4
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    Embedded Plate Connection Between Hollow-Core Slabs and Concrete Walls
    (2023-08) Jackman, Kal
    In current practice, hollow-core slabs are connected to the top of cast-in-place walls using dowel or welded connections. The existing research on these connections is minimal, and their design capacity is limited, which created the need for a new connection that has a more efficient installation and an increased design capacity. This research project investigated a new slab-to-wall connection that consisted of an embedded steel plate and stud in the hollow-core. The capacity of the plate assembly embedded in a hollow-core slab was established by directly loading the assembly until steel or concrete failure. Proof-of-concept subassembly testing was conducted on hollow-core slabs connected to cast-in-place walls; the setup mimicked assembly at a jobsite. Capacity of the subassembly was established by applying load until the hollow-core slab, wall, or anchor failed. Results indicated that the embedded steel plate plus stud connection had a capacity that ranged from 8.6 to 33.5 kips when load was applied in various directions. The subassembly results indicated that the wall typically failed first, when subjected to applied loads that ranged from 2.5 to 19.8 kips. These results indicated that the proposed embedded steel plate and stud connection was robust enough for use in real-world applications.
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    Load Rating of Concrete Slab-span Bridges
    (2022-05) HILL, KENDALL
    Three slab-span bridges crossing Shingle Creek in Brooklyn Center, MN have poor AASHTO load rating factors for certain truck configurations. Characterization of load distribution is useful for determining the load rating of bridges, but results in the literature have shown that the AASHTO code results in conservative load rating factors. The focus of this study was to determine if the load rating of the three concrete slab-span bridges was conservative and could be improved using results from live load testing and finite element analysis. Field testing utilized a suite of instrumentation that included displacement transducers, strain gauges, accelerometers, and tiltmeters. A three- dimensional solid-element finite element model was used to determine an expected range of behaviors and corroborate the field data regarding how load distributed when placed near and away from a barrier. Additionally, a method for developing a simple plate model of slab span bridges was developed considering in-situ material properties and effects of secondary elements such as barriers. Results indicated that the AASHTO load rating is conservative, and an improved rating factor could be obtained considering the field test data and computational modeling results.
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    Shear Distribution in Prestressed Concrete Girder Bridges
    (2015-10) Dymond, Benjamin
    As shear requirements for prestressed concrete girders have changed, some structures designed using older specifications do not rate well with current methods. However, signs of shear distress have not been observed in these bridge girders and they are often deemed to be in good condition. The primary objective of this research program was to investigate the accuracy of existing shear distribution factors, which are used to estimate bridge system live load effects on individual girders, and provide recommendations on shear distribution to be used in Minnesota with three components: a full-scale laboratory bridge subjected to elastic and inelastic behavior, field testing of bridges, and a numerical parametric study. Results from the components were integrated to develop recommendations for rating prestressed concrete girder bridges. Laboratory bridge inelastic testing indicated shear force redistribution after cracking and before ultimate failure. Use of elastic distribution factors is conservative for shear distribution at ultimate capacity. Elastic laboratory testing was used to validate the finite element modeling technique and study the behavior of a traffic barrier and end diaphragm, which affected shear distribution. Ignoring the effects of the barrier was conservative and ignoring the effects of the end diaphragm was slightly inaccurate by 4 to 6 percent but was warranted for simplicity. Parametric study results indicated that a ratio of longitudinal stiffness to transverse stiffness could be used as a screening tool. If the stiffness ratio was less than 1.5, shear demand from a simple, conservative grillage analysis may be more accurate than shear demand from AASHTO distribution factor methods. Grillage analysis shear demand results due to permit trucks may also be more accurate, regardless of the screening tool ratio.
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    Variation In Web-Shear Capacity of Hollow-Core Slabs With Filled Cores
    (2020-06) Asperheim, Scott
    The web-shear capacity of hollow-core slabs both with and without concrete or grout core-fill material, as well as slabs that were cast with a solid extruded core (i.e., with one of the voids omitted), was experimentally investigated using two different hollow-core slab geometries to evaluate how the fill material affected the shear capacity. The shear demand at failure was compared to five different methods of predicting the shear capacity of hollow-core slabs: ACI 318 (2014), the AASHTO (2017) sectional design model, a method proposed by Lin Yang (1994), the EN 1168 (2011) general method, and the EN 1168 (2011) simplified method. Additionally, a web-shear capacity prediction method was proposed based on the ACI-ASCE Committee 326 (1962) report on shear and diagonal tension.