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No description available.

Single plate shear connections are designed to have sufficient strength to resist the shear force and moment transferred from the beam. The connections must also provide sufficient ductility to allow the beam end to rotate freely. In the United States the current recommended design method is found in the AISC 13th Edition Steel Construction Manual (2005b). The limited experimental work which led to the current method necessitated additional single plate shear connection investigations. This paper summarizes the results and analysis of eight full scale single plate shear connections tested at Virginia Polytechnic Institute and State University. The test setup consisted of a test beam attached to a test column with a single plate shear connection at one end and supported by a roller at the other end. The single plate was welded to the column flange and bolted to the beam web. Load was applied to the test beam at third points until failure of the connection or test beam. The current design method used in the United States was examined with respect to the connection tests performed. In particular, the ultimate shear strength and the rotational capacity were investigated. Suggestions are made regarding changes to the method and further research. / Master of Science

Safety is the most important aspect to the mining industry. Research having a direct and positive impact on mine safety is always needed and should be supported. There are several different types of primary roof supports that are used to try to maintain stable mine workings in order to extract the coal safely. The majority of roof bolts installed annually in underground coal mines in the USA use resin cartridges (Tadolini, 2006). The standard roof bolt used is a fully grouted resin rebar bolt. This is considered a passive (un-tensioned) support. Technological advances in roof support anchored with resin grout systems have resulted in the development of supports that are active (tensioned during installation). Generally it is thought that active anchors are superior in performance as roof support except in highly laminated weak roof. The assumption is that since an active system applies some pre-tension to the roof, it will provide a more stable roof beam. There is, however, a lack of real data to back up this perception. A systematic attempt is through this project that addresses this knowledge gap. Without a clear idea on how different roof bolt systems work in-situ, the consequences could have a significant impact on the safety of the miners working underground as well as production costs. Supports are now often only chosen based on perceived ideas instead of real data. Such assumed superior performance of the support system could lead to false economy. Essentially, it needs to be demonstrated to what degree or under what conditions, if any, these technological advances in roof support improve ground conditions and opening stability and ultimately improve the safety of the miners. There is an argument regarding whether passive bolts could truly be better than active bolts. The focus is centralized towards a cost and performance issue. The overall goal of the proposed project was to develop an understanding of the interaction between different roof bolt types and the immediate strata in a longwall headgate as the longwall face progresses. In order to monitor the interactions between the strata and roof bolts, specially instrumented bolts were installed with six strain gauges that were electronically accessed. A look into the initial bolt loads was used to compare three different bolt types (both tensioned and untensioned) upon installation. These loads continued to be monitored and analyzed as the longwall face approached and passed the location of the instrumented bolts. Along with analyzing instrumented bolt data compared to a passing longwall face, a limited finite element model was set up within Flac3D to represent real conditions, and compare the in situ data collected to the computer outputs in order to establish beginning phases of validating the results.

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M.Tech. / The field of study is of a multidisciplinary nature and involves aspects of Mechanical Engineering Design, Materials Technology and Rock Mechanics. When rock bursts occur the rock mass moves at high velocities and the resulting impulsive load often leads to brittle fracture of fully grouted steel bars. It was therefore decided to develop a new product that would combine the strength of steel and the yielding ability of polyurethane. Such a product is envisaged to play an important role in the correct design of tunnel support. In optimizing the design of a polyurethane and steel combination, three important parameters have to be optimized simultaneously...

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Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1989. / Vita. Abstract. Includes bibliographical references (leaves 76-77). Also available via the Internet.

Thesis (Ph. D.)--University of Wisconsin, 1967. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

Rock bolts have been extensively used as a support element in coal mines in the US for about 40 years. Longwall development and partial extraction room-and-pillar mining systems now rely heavily on fully-grouted roof bolts as the primary support with as needed inclined bolts, trusses, and cable bolts as secondary support. These two coal mining systems develop 3- and 4-way intersections during extraction processes. A study of Illinois (2004-2008) and US coal mines found that over 70% of roof falls occurred at intersections. It is therefore necessary to perform additional research in stress and displacement distributions around intersections and then design support systems to improve stability of intersections. This thesis research, in cooperation with a bolt supplier and NIOSH, analyses the stress and strain redistribution in and around intersections in typical lithologies in the Illinois Basin coal mines with the goal to develop a better understanding of failure initiation and propagation mechanisms with and without roof supports. Analyses were corroborated with field observations wherever possible. Non-linear continuum analyses using the Generalized Hoek-Brown failure criterion with rock mass properties is the foundation for these analyses. The first task (Task 1) toward these goals was to develop rock mass properties from available laboratory data using estimates of Geological Strength Index (GSI) for different lithologies. An important subtask was to perform an error analysis in estimates of rock mass properties assuming an amount of error in GSI estimates. Analyses and field observations were done for typical 4-way intersections at two mines in southern Illinois operating at depths of 150 m and 80 m, respectively in the No. 6 coal seam, which averages 1.8 m in thickness. Pre-mining horizontal stresses of 7.58 MPa and 4.13 MPa were applied in the E-W and N-S directions. These coal companies provided geologic logs and rock mechanics data for roof and floor strata. Rock mass engineering properties for different roof and floor lithologies were developed using estimated values of Geological Strength Index (GSI), and Hoek-Brown (H-B) rock mass failure parameters. A recent laboratory study provided normal and shear stiffness properties of the immediate roof interfaces within the bolting range of 1.8 m. MSHA-approved roof support plans were used for initial modeling. Short Encapsulation Pull Test (SEPT) data provided by bolt suppliers in the region were used to assign bolting system stiffness and strength parameters. Task 2 analyzed normal and shearing stresses and strains in and around mine intersections for typical pre-mining stress fields and then identified critical areas of failure initiation and progressive failure propagation. Failure initiation was hypothesized to occur for critical values of compressive (1 mm/m), tensile (0.5 mm/m), and shearing (0.5 mm/m) strains based on a review of laboratory stress-strain properties. This approach allows quantifying areas in and around an intersection where failures are likely to initiate with and without artificial supports. It computes three reinforcement factors with and without supports: reinforcement against tensile (RFT), compressive (RFC) and shearing (RFSS) strains. Task 3 assessed the performance of currently practiced roof support plans and identified where inadequacies exist and how they could be improved through spatial distribution of supports and their characteristics. Analyses were completed for two mines with one orientation of pre-mining horizontal stress field. The next logical step (Task 4) was to extend analyses in Task 3 to assess the effect of maximum compressive stress orientation in relation to entry direction (0o, 30o, 60o & 90o) and different cut sequences and their effect on changes in failure initiation and failure propagation mechanisms. Numerical analyses have shown that stress and strain distributions are significantly different when the cut sequence is included in models. For a horizontal stress ratio of two (2), the 60o orientation provided maximum stability. Separate models with all cuts excavated simultaneously corresponded well with the well-established NIOSH software AHSM and previous research. The effect of cut sequence combined with the directional effect of pre-mining stresses becomes evident from the dissimilar results. A separate statistical study was conducted on 211 SEPT test data provided by a roof support manufacturer and marketing company in the region. Goals were to analyze the database for grip factor (GF) and anchorage stiffness (AS) characteristics using histograms and frequency distributions and, perform regression analyses to relate GF and AS values on the basis of height above coal seam and bolt diameter. Results were used for one stochastic run with variable GF and AS values assigned to different bolts in a roof control plan. Results indicated Gamma distribution best fitted AS and GF data. It was thought that the reinforcement factor for such a bolting layout would be more realistic than assigning a single value of GF and AS to bolts in the model.