Browsing by Subject "Strength"
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Item ASR/DEF-damaged bent caps: shear tests and field implications(2009-12) Deschenes, Dean Joseph; Bayrak, Oguzhan, 1969-; Folliard, Kevin J.Over the last decade, a number of reinforced concrete bent caps within Houston, Texas have exhibited premature concrete damage (cracking, spalling and a loss of material strength) due to alkali-silica reaction (ASR) and/or delayed ettringite formation (DEF). The alarming nature of the severe surface cracking prompted the Houston District of the Texas Department of Transportation to initiate an investigation into the structural implications of the premature concrete damage. Specifically, an interagency contract with the University of Texas at Austin charged engineers at Ferguson Structural Engineering Laboratory to: 1. Establish the time-dependent relationship between ASR/DEF deterioration and the shear capacity of affected bridge bent caps. 2. Develop practical recommendations for structural evaluation of in-service bridge bent caps affected by ASR and/or DEF. To accomplish these objectives, six large-scale bent cap specimens were fabricated within the laboratory. Four of the specimens (containing reactive concrete exposed to high curing temperatures) represented the most severe circumstances of deterioration found in the field. The remaining two specimens (non-reactive) provided a basis for the comparison of long-term structural performance. All of the specimens were subjected to a conditioning regimen meant to foster the development of realistic ASR/DEF-related damage. Resulting expansions were characterized over the course of the study through a carefully-planned monitoring program. Following a prolonged exposure period, three of the six bent cap specimens (representing undamaged, mild, and moderate levels of deterioration) were tested in shear. Observations made over the course of each test captured the service and ultimate load effects of ASR/DEF-induced deterioration. Six shear-critical spans were tested prior to this publication: three deep beam and three sectional shear tests. The remaining six shear spans (contained within the remaining three specimens) were retained to establish the effects of severe deterioration through future shear testing. Subsequent analysis of the expansion monitoring and shear testing data provided much needed insight into the performance and evaluation of ASR/DEF damaged bent structures. The results ultimately formed a strong technical basis for the preliminary assessment of a damaged bent structure within Houston, Texas.Item Design of reinforced concrete inverted-T beams for strength and serviceability(2013-05) Larson, Nancy Anne, 1986-; Bayrak, Oguzhan, 1969-Significant diagonal cracking in reinforced concrete inverted-T straddle bent caps has been reported throughout the State of Texas. Many of the distressed structures were recently constructed and all have been in service for less than two decades. The unique nature of the problem prompted a more detailed look into the design and behavior of such structural components. Strut-and-tie modeling is currently recommended for design of deep (rectangular) beams, but its application to more complex structures has not been fully explored. Due to concerns with current design provisions the application of strut-and-tie modeling to inverted-T beams was investigated along with serviceability-related considerations in this dissertation. An experimental study was conducted in which thirty-three reinforced concrete inverted-T beam tests were conducted. The effects of the following variables were evaluated: ledge depth and length, quantity of web reinforcement, number of point loads, member depth, and shear span-to-depth ratio. A strut-and-tie design method proposed by Birrcher et. al (2009), initially calibrated for compression-chord loaded deep beams, was investigated. It was concluded that the strut-and-tie method was a simple and accurate design method, and it was recommended for use in inverted-T beam design. A vi recommendation was also made for the amount of minimum web reinforcement needed for strength and serviceability considerations. A simple service-load check was proposed for the purpose of limiting diagonal cracking under service loads. Finally, a chart was created to aid in the evaluation of distressed, diagonally-cracked inverted-T bent caps in the field.Item Effects of handle height and COF on maximal strength generation during push/pull activities(Texas Tech University, 2006-08) Kafka, Matthew D.; Woldstad, Jeffrey C.; Smith, James L.; Collins, Terry R.Manual materials handling, or MMH, is the process of a human lifting, lowering, pushing, pulling, or conducting any similar task in which an object is moved through space solely by the power of that human. Historically, manual material handling is a known contributor to the number of accidents and/or injuries that occur in industry, especially injuries related to the low back. Employee well being and safety are precursors for a productive and fully operational employee. Therefore it is advantageous to prevent employee injuries by designing and implementing ergonomically designed equipment and safety procedures which reduce the risk of musculoskeletal injuries. The following analysis studied the effects of handle height and coefficient of friction and whether or not there was an interaction between the two variables. An isometric strength testing fixture was used to measure the push/pull hand forces. The apparatus had a stationary bar, which was attached to a Bertec force plate, which was used by the subjects to input their force capabilities. Alternative Hypothesis one validated results that for all push and pull trials, handle height was the significant factor that affected force generation. Subjects were able to produce a maximum force when the handle height was set at the 66cm level. Alternative Hypothesis two results indicate that COF was a significant factor in the pull trials, while not as important in the push trials. Alternative hypothesis three concluded that the interaction between the 66cm handle height and high COF produced the highest amount of force.Item The impact of foam rolling on explosive strength and excitability of the motor neuron pool(2013-08) Abels, Kristin Marie; Abraham, Lawrence D.To assess acute performance-related effects of foam rolling, this study investigated the immediate effects of a standard foam rolling protocol on explosive strength of the plantarflexors and alpha motor neuron excitability in the soleus. Explosive strength was measured via vertical jump height (JUMP) and the Reactive Strength Index (RSI) obtained from a single leg drop jump. Alpha motor neuron excitability was measured by H reflex amplitude as H wave to M wave ratio (HM) obtained from the soleus muscle. JUMP and RSI measures were analyzed from nineteen subjects (12 male, 7 female) HM data were analyzed from 15 subjects (9 male, 6 female). Subjects attended one day of practice and instruction for the single leg drop jump and one day for data collection. One leg was randomly assigned to be the test leg (FL) and the other as the control (NL). The reported dominant leg and gender were also recorded for each subject. Subjects performed two single leg drop jumps per leg from a box height of 30 cm and then 10 soleus H reflexes were obtained. The intervention, which followed standard professional guidelines, consisted of 2.5 minutes of foam rolling for the FL and rest for the NL, followed by a 5 minute warm up on a cycle ergometer. The best jump and the average HM ratio were chosen for analysis. For each variable a post/pre ratio was calculated for statistical analysis. A 2x2x2 factor ANOVA with repeated measures on both factors was used for each variable. Analysis revealed no statistically significant differences for any of the variables, either as main effects or any of the interaction effects. Subjects trended towards a slightly larger post-intervention decrease in JUMP and RSI for the FL than the NL but this was not significant. It was concluded that a 2.5 minute intervention of foam rolling had no acute effect on explosive strength of the plantarflexors or alpha motor neuron excitability of the soleus.Item INFLUENCE OF MATRIC SUCTION AND SATURATION ON COMPRESSIVE AND FLEXURAL STRENGTH OF UNSTABILIZED COMPRESSED EARTH BLOCK(2013-05) Gaikwad, Aditya; Tate, Derrick; Lawson, William D.; Bae, Sang-WookEarth materials have been used as a construction material for centuries. But systematic modern research for compressed earth dates back to the early 60’s. Compressed earth has shown to be a very durable material. This is evident from all the ancient structures, which have stood the test of time. Previous experiments with compressed earth have studied the properties of compressed earth blocks. This research builds on that knowledge to study influence of matric suction and initial moisture content on the compressive and flexural strengths of the blocks. The soil was procured from a landfill site near Lubbock international airport. Tests were performed to analyze the soil type. Blocks were then made using the compressed earth block manufacturing machine available at Texas Tech University. Experiments were carried out to study the compressive and flexural strengths of the blocks when cured in two different relative humidity conditions. These blocks were made at three different initial moisture contents. The results show an increase in compressive strength with an increase in suction. The results for the flexural strength data were different from expected, showing a decrease in flexural strength with an increase in matric suction. The change in the strength was also studied relative to the change in the suction and saturation.Item Neck strength and concussion in NCAA division I football(Texas Tech University, 2007-05) Black, Sandra R.; Boros, Rhonda L.; Miller, John; Henry, Judith; Munger Jr., LarryPurpose: Biomechanical analysis has indicated that concussions will occur secondary to linear and or rotational acceleration-deceleration changes of the head, as well as axial compression to the cervical spine. Researchers have revealed the importance of neck strength in force absorption rates with football players, but have failed to report any definitive relation between weak or untrained musculature and concussion. Through proper neck strengthing regimens, football athletes may train neck muscles to absorb potentially damaging changes in momentum associated with mild traumatic brain injury. Methods: Twelve division I football athletes from Texas Tech University, who had sustained at least a grade one concussion in the last three years, were compared to twelve matched non-concussed football players based on height, weight, experience, and player position. Subjects’ weight charts containing six consecutive weeks of work out routines preceding concussion were analyzed. A normalized volume load (NVL) for each workout on the weight training days preceding concussion was compared between groups and individuals. The NVL data were compared between subjects and across weeks using a 2x6 mixed design ANOVA with repeated measures, and .05 was selected as the level of statistical significance. Results: No statistically significant relations between the concussed and non-concussed participants (p>0.05) were observed. Descriptive statistics for the concussed versus non-concussed group mean + SD NVL were: WK1) 15.2+8.7 vs. 13.0+9.1; WK2) 18.8+8.9 vs. 15.9+6.8; WK3) 15.2+9.0 vs. 14.8+5.9; WK4) 15.0+9.3 vs. 13.6+7.5; WK5) 16.8+9.2 vs. 17.9+8.0; and WK6) 18.1+9.1 vs. 18.0+9.1. Week six (WK6) represents the week the concussion occurred. Eight of 12 concussed players were on defense. The concussed group consisted of four defensive backs (DBs), two linebackers, two defensive tackles, one wide receiver, two offensive linemen, and one long snapper. More concussions were observed in upper classmen (i.e., juniors and seniors), as would be expected due to a greater percentage of upper-class first string and starting players. Conclusion: Comparisons of neck musculature training regimes, rather than actual strength measurements, may not be sufficient to identify a significant relation between training and concussion incidence. Future studies should directly measure neck strength, rather than rely on training records. Consistency in training protocols and comparison of concussion incidence between football programs that implement different training routines (e.g. periodization, isometric isolations, and power enhancing strength) should also be investigated. Future research may also measure cervical neck strength throughout the season as well as after concussion to identify any consistent periods of weakness that may correlate with periods of increased concussion incidence.Item Strength, stiffness, and damage of reinforced concrete buildings subjected to seismic motions(2016-05) Kwon, Jinhan; Ghannoum, Wassim M.; Jirsa, James O.; Bayrak, Oguzhan; Hrynyk, Trevor; Sen, Mrinal K.Current analytical tools were calibrated mainly using pseudo-static experimental investigations of individual structural components. Relatively few tests have been performed on reinforced concrete structural systems under realistic boundary conditions and even fewer exist that were conducted dynamically due to the high costs and experimental challenges. Thus, the structural engineering field has resorted to a number of extrapolations from limited test data to form analytical models of structural systems they design. It is therefore no surprise that blind prediction contest results for structural strength and deformation are typically several times higher and lower than those from experiments. A complete system of a full-scale, four-story, reinforced concrete structure was tested under increasing seismic excitations, to near collapse damage states, one the National Research Institute for Earth Science and Disaster Prevention (NIED)/E-Defense shaking table in Japan. A moment frame system was adopted in one direction and a pair of shear walls incorporated in the exterior frames in the other direction. Wherever possible, minor adjustments to the designs were made to bring the final structures closer to U.S. seismic design provisions. No other tests currently exist that provide behavioral data about a complete, seismically detailed, reinforced concrete structural system tested under such realistic boundary conditions. Comprehensive and in-depth analyses were performed in light of the NIED/E-Defense test data to 1) assess the validity of current behavioral knowledge and design codes; 2) to assess the accuracy of current analytical methods for this common type of structure; 3) to recommend improvements and ways forward on both fronts. Implications of test results to U.S. seismic provisions and recommendations for estimating structural strength and stiffness of reinforced concrete buildings were made based on comparison between the estimates from the current analytical methods and the actual seismic behavior of the NIED/E-Defense test data.Item Strut-and-tie model design examples for bridge(2011-12) Williams, Christopher Scott; Bayrak, Oguzhan, 1969-; Ghannoum, Wassim M.Strut-and-tie modeling (STM) is a versatile, lower-bound (i.e. conservative) design method for reinforced concrete structural components. Uncertainty expressed by engineers related to the implementation of existing STM code specifications as well as a growing inventory of distressed in-service bent caps exhibiting diagonal cracking was the impetus for the Texas Department of Transportation (TxDOT) to fund research project 0-5253, D-Region Strength and Serviceability Design, and the current implementation project (5-5253-01). As part of these projects, simple, accurate STM specifications were developed. This thesis acts as a guidebook for application of the proposed specifications and is intended to clarify any remaining uncertainties associated with strut-and-tie modeling. A series of five detailed design examples feature the application of the STM specifications. A brief overview of each design example is provided below. The examples are prefaced with a review of the theoretical background and fundamental design process of STM (Chapter 2). • Example 1: Five-Column Bent Cap of a Skewed Bridge - This design example serves as an introduction to the application of STM. Challenges are introduced by the bridge’s skew and complicated loading pattern. A clear procedure for defining relatively complex nodal geometries is presented. • Example 2: Cantilever Bent Cap - A strut-and-tie model is developed to represent the flow of forces around a frame corner subjected to closing loads. The design and detailing of a curved-bar node at the outside of the frame corner is described. • Example 3a: Inverted-T Straddle Bent Cap (Moment Frame) - An inverted-T straddle bent cap is modeled as a component within a moment frame. Bottom-chord (ledge) loading of the inverted-T necessitates the use of local STMs to model the flow of forces through the bent cap’s cross section. • Example 3b: Inverted-T Straddle Bent Cap (Simply Supported) - The inverted-T bent cap of Example 3a is designed as a member that is simply supported at the columns. • Example 4: Drilled-Shaft Footing - Three-dimensional STMs are developed to properly model the flow of forces through a deep drilled-shaft footing. Two unique load cases are considered to familiarize the designer with the development of such models.Item Temperature, stress, and strength development of early-age bridge deck concrete(2011-08) Pesek, Phillip Wayne; Folliard, Kevin J.; Drimalas, ThanosIn bridge deck concrete, early-age cracking can lead to substantial serviceability and structural integrity issues over the lifespan of the bridge. An understanding of the temperature, stress, and strength development of concrete can aid determining the early-age cracking susceptibility. This project, funded by the Texas Department of Transportation, evaluated these properties for various bridge deck materials and mixture proportions. The research presented in this thesis involved a laboratory testing program that used a combination of semi-adiabatic calorimetry, rigid cracking frame, free shrinkage frame, and match cured cylinder testing program that allowed the research team to simulate the performance of common bridge deck mixture designs under hot and cold weather conditions. In this program, the semi-adiabatic calorimetry was used, with previously generated models, to generate the temperature profile of the mixture. The rigid cracking frame and free shrinkage frame were used to evaluate the restrained stress development and the unrestrained volume changes, respectively, under the simulated temperatures. The match-cure cylinder testing program allowed the research team to generate a strength development profile for the concrete mixtures under the various simulated temperature profiles. Results from the laboratory program revealed that in hot weather simulations, ground granulated blast furnace slag mixtures developed the lowest stress / strength ratios, and in cold weather simulations, Class F fly ash mixtures developed the lowest stress / strength ratios. In general, use of SCMs and limestone coarse aggregate results in mixtures that generate less heat and lower stress / strength ratios. Isothermal testing showed that shrinkage reducing admixtures were effective in reducing early-age strains from chemical shrinkage. In addition to the laboratory testing program, a field testing program was completed to measure the temperature development of four bridge decks during the winter and summer months. The recorded concrete temperatures and the effects of the environmental conditions at the time of the pour will aid in the calibration and validation of the temperature prediction component of ConcreteWorks for bridge deck construction. In addition, experience gained through these field pours resulted in an optimized instrumentation procedure that will aid in the successful collection of data in future projects.