Laser Welded Steel Sandwich Panel Bridge Deck Development: Finite Element Analysis and Stake Weld Strength Tests
Author: Caccese, Vincent | Size: 4.34 MB | Format:PDF | Quality:Original preprint | Publisher: University of Maine, Orono | Year: 2009 | pages: 108
This report summarizes the analysis of laser welded steel sandwich panels for use in bridge structures and static testing of laser stake welded lap shear coupons. Steel sandwich panels consist of two face sheets connected by a relatively low-density core resulting in high strength and stiffness, which leads to promising design advantages. Steel sandwich panels offer substantial resistance to static and dynamic loads due to their high stiffness and substantial energy absorbing capacity. Panels of this kind are of interest for potential use in bridges for deck replacement. They are especially efficient in resisting dynamic events such as fatigue, impact or shock loading. A verification study is performed comparing finite element analysis and an analytical model to an experimental study documented in the literature. Results demonstrate good agreement between the approaches. Modeling techniques are developed from the verification study. Finite element analyses are subsequently employed to study the response of a laser welded steel sandwich panel case study of a deck replacement for a steel bridge located in Gardiner, Maine. The deck design results in a stiff structure that has a deflection of 1/1500 of the span at a depth of 7.25 inches. Structural response of stake welds was also investigated experimentally in a single lap shear configuration. Multiple pass welds consisting of 2 and 4 stake weld passes were fabricated and tested to assess the process of using multi-passes to increase weld resistance.
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Posted by: mahyarov - 11-13-2012, 10:24 AM - Forum: Steel
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Fatigue Life of Steel Base Plate to Pole Connections for Traffic Structures
Author: Stam, Andrew Richman, Nicholas Pool, Charles Rios, Craig Anderson, Thomas Frank, Karl | Size: 3.77 MB | Format:PDF | Quality:Original preprint | Publisher: University of Texas, Austin | Year: 2011 | pages: 165
This is a final report of an extensive experimental and analytical examination of the fatigue behavior of the welded end connection used on high-mast light structures and traffic signal masts. The weld details commonly used for these connections produce very poor fatigue performance. Their performance is a function of base plate stiffness, weld type and geometry, and number of anchor bolts. Older connection designs produced very poor fatigue performance far below the lowest American Association of State Highway and Transportation Officials (AASHTO) fatigue category. These connections can be improved by increasing the base or end plate thickness, improving weld details, and other geometric considerations. Due to the interaction of the overall connection geometry upon fatigue performance, the fatigue performance of the connection cannot be classified by simply the type of connection. The fatigue life can be improved to fatigue performance comparable to Category B but a similar connection with a thinner base plate can produce fatigue life of Category E. Recommended connections and their corresponding fatigue strength are given as well as recommended fabrication and welding specifications.
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Posted by: mahyarov - 11-13-2012, 10:21 AM - Forum: Steel
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Fatigue Failure and Cracking in High Mast Poles
Author: Goyal, Raka Dhonde, Hemant B Dawood, Mina | Size: 2.71 MB | Format:PDF | Quality:Original preprint | Publisher: University of Houston | Year: 2012 | pages: 272
This report presents the findings of a comprehensive research project to investigate the fatigue cracking and failure of galvanized high mast illumination poles (HMIP). Ultrasonic inspection of poles throughout the state has revealed the presence of weld toe cracks at the shaft-to-base-plate connections of some galvanized poles that the Texas Department of Transportation (TxDOT) owns. However, the effect of these galvanization-induced cracks on the fatigue life of the poles has not been clearly defined. The first phase of this research involved extensive review of published and unpublished data, to identify key factors that contribute to galvanization-induced cracking. Best fabrication practices to minimize such cracking are recommended. In the second phase, a comprehensive reliability analysis of several TxDOT pole configurations was conducted for different regions in Texas to predict the fatigue lives of the cracked poles. Critical pole configurations and locations are identified to facilitate cost-effective decisions related to inspection, repair, and replacement of poles.
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Posted by: mahyarov - 11-13-2012, 09:09 AM - Forum: Concrete
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Validation and Practical Procedure for Vibrational Evaluation of Tendons
Author: Sagues, Alberto A | Size: 1.62 MB | Format:PDF | Quality:Original preprint | Publisher: University of South Florida, Tampa | Year: 2008 | pages: 189
Vibrational testing of tension to identify potentially distressed external tendons of post-tensioned segments and columns has been successfully used in major Florida Department of Transportation (FDOT) bridges. This investigation provided validation of basic assumptions and verification of tension obtained by the vibration method against independent load cell measurements with tendon segments of size, length, and tension levels comparable to those used in actual structures. Measurements were conducted in a specially built tendon test facility with 12-strand tendons up to nearly 10 m (400 in.) long, some including a deviation block. Tension estimated from vibration tests was on average within ~6% of load cell measurements, after correction for the effect of metal pipe ends in some cases. Upon simulated strand failures at the anchorage area there was tension loss that was tracked adequately in nearly all cases by the vibration tests. Advanced data processing methods were developed to perform rapid evaluation of data from large populations (thousands) of tendons in actual bridges. Vibration test field equipment was developed for simplified operation and analysis procedures. A portable field equipment prototype was designed and constructed to permit testing by a single operator. Extensive vibration tests of tendons were conducted in the segmental approaches of the Sunshine Skyway Bridge, revealing generally normal tension levels but flagging specific tendons with fringe performance for subsequent inspection. A user-oriented summary of findings and applications is provided.
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Posted by: mahyarov - 11-13-2012, 09:06 AM - Forum: Concrete
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Flexural and Tensile Properties of Thin, Very High-Strength, Fiber-Reinforced Concrete Panels
Author: Roth, Michael J | Size: 4.85 MB | Format:PDF | Quality:Original preprint | Publisher: U.S. Army Engineer Research and Development Center | Year: 2008 | pages: 191
This research was conducted to characterize the flexural and tensile characteristics of thin, very high-strength, discontinuously reinforced concrete panels jointly developed by the U.S. Army Engineer Research and Development Center and U.S. Gypsum Corporation. Panels were produced from a unique blend of cementitious material and fiberglass reinforcing fibers, achieving compressive strength and fracture toughness levels that far exceeded those of typical concrete. The research program included third-point flexural experiments, novel direct tension experiments, implementation of micromechanically based analytical models, and development of finite element numerical models. The experimental, analytical, and numerical efforts were used conjunctively to determine parameters such as elastic modulus, first-crack strength, post-crack modulus and fiber/matrix interfacial bond strength. Furthermore, analytical and numerical models implemented in the work showed potential for use as design tools in future engineered material improvements.
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Post-tensioned (PT) bridges are major structures that carry significant traffic. These bridges are designed and constructed because they are economical for spanning long distances. In Texas, there are several signature PT bridges. In the late 1990s and early 2000s, several state highway agencies identified challenges with the PT structures: mainly corrosion of the PT strands. The Texas Department of Transportation (TxDOT) performed some comprehensive inspections of their PT bridges. A consultant’s report recommended that all ducts be re-grouted. However, the environment in Texas is very different than the environments in which the corrosion of the PT strands were observed. The objective of this research was to evaluate the corrosion activity of strands for PT structures and to correlate this corrosion activity with general environmental and void conditions. To achieve this objective, time-variant probabilistic models were developed to predict the tension capacity of PT strands subjected to different environmental and void conditions. Using these probabilistic models, time-variant structural reliability models were developed. The probability of failure of a simplified PT structure subjected to HS20 and HL93 loading conditions was assessed. Both flexural failure and serviceability were assessed. Results indicate that the presence of water and chlorides can lead to significant corrosion rates and failure is dependent on this corrosion activity and the number of strands exposed to these conditions. These results are presented in Volume 1 of this report. To assist TxDOT with developing a plan to mitigate this corrosion, studies were performed to assess repair grout materials, inspection methods, and repair methods. In addition, a general methodology is presented on optimizing repairs. These topics are presented in Volume 2 of this report. An Inspection and Repair Manual was also developed from this research and is presented in a separate report. Results indicate that TxDOT should prevent water and chlorides from infiltrating the tendons — this can be achieved in part by repairing drain lines, ducts, and protecting anchor heads as these conditions can lead to early failure of PT bridges. Recommendations on inspections, repairs, and materials are provided, however, further research on the potential formation of galvanic coupling of strands embedded in both existing and new repair grouts need to be assessed.
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Post-tensioned (PT) bridges are major structures that carry significant traffic. PT bridges are economical for spanning long distances. In Texas, there are several signature PT bridges. In the late 1990s and early 2000s, several state highway agencies identified challenges with the PT structures, mainly corrosion of the PT strands. The Texas Department of Transportation (TxDOT) performed some comprehensive inspections of its PT bridges. A consultant’s report recommended that all ducts be re-grouted. However, the environment in Texas is very different than the environments in which the corrosion of the PT strands were observed. The objective of this research was to evaluate the corrosion activity of strands for PT structures and to correlate this corrosion activity with general environmental and void conditions. To achieve this objective, time-variant probabilistic models were developed to predict the tension capacity of PT strands subjected to different environmental and void conditions. Using these probabilistic models, time-variant structural reliability models were developed. The probability of failure of a simplified PT structure subjected to HS20 and HL93 loading conditions was assessed. Both flexural failure and serviceability were assessed. Results indicate that the presence of water and chlorides can lead to significant corrosion rates and failure is dependent on this corrosion activity and the number of strands exposed to these conditions. Volume 1 of this report presents these results. To assist TxDOT with developing a plan to mitigate this corrosion, studies were performed to assess repair grout materials, inspection methods, and repair methods. In addition, a general methodology is presented on optimizing repairs. These topics are presented in Volume 2 of this report. An Inspection and Repair Manual was also developed from this research and is presented in a separate report. Results indicate that TxDOT should prevent water and chlorides from infiltrating the tendons; this can be achieved in part by repairing drain lines and ducts and protecting anchor heads, as these conditions can lead to early failure of PT bridges. Recommendations on inspections, repairs, and materials are provided; however, further research on the potential formation of galvanic coupling of strands embedded in both existing and new repair grouts needs to be assessed.
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Current codes recommend large amounts of shear reinforcement for reinforced concrete beam-column joints causing significant congestion. This research aims at investigating experimentally and numerically the efficiency of using studs with a head at each end in lieu of conventional closed hoops in reinforced concrete beam-column joints. The proposed reinforcement reduces congestion and ensures easier assembly of the reinforcing cage, saving labour cost and enhancing performance of the joint. Based on this research, a recommended arrangement and detailing of headed studs and their design for exterior beam-column joint are presented. The experimental investigation consisted of testing ten full-scale beam-column joint specimens under quasi-static cyclic loading. The specimens represented an exterior beam-column joint subassembly isolated at the points of contra-flexure from a typical multi-storey, multi-bay reinforced concrete frame. A test setup was developed to simulate the lateral inter-storey drift. The test parameters included: the type, arrangement and amount of shear reinforcement, the load history and rate of loading, and the amount of reinforcement for out-of-plane confinement of the joint. Envelopes of the hysteretic behaviour of the specimens and the joint deformation under shear stress are presented. The stiffness degradation, the strain levels in the joint reinforcement, the contribution of joint, beam, and column to the inter-storey drift, and the energy dissipation were compared. All the test specimens reinforced with headed studs in the joint achieved considerable enhancement in their behaviour under cyclic loads and exhibited a performance close to that of a joint reinforced with closed hoops and cross ties according to the code. All the specimens with adequate out-of-plane confinement had an equivalent behaviour compared with the code-based specimen and achieved a desirable mode of failure. Use of double-headed studs proved to be a viable option for reinforcing exterior beam-column joints. A three dimensional finite element model was developed. The concrete material model used combines constitutive models for cracking and plasticity. The model was verified against the experimental results. Good agreement was found between the experimental and numerical hysteretic behaviour. The strengths and weaknesses of the model were identified. The model was used to study the effect of various parameters on the joint behaviour including: concrete strength, column load and out-of-plane confinement.
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During the Ismit (Kocaeli) earthquake of 17 August 1999, a 115m high reinforced concrete chimney or heater stack, located at the Tüpras Refinery, collapsed. The falling debris cut 63 pipes, which contributed to interrupted production for more than 14 months. This stack was designed and constructed according to international standards and is representative of similar structures at refineries throughout the world, including those in earthquake-prone regions. It was distinguished from similar stacks at the site by a much larger rectangular opening for the flue duct, circumscribing a horizontal arc of about 50°. The opening was located about 1/3 of the height above the base and appeared to be the region of initiation of the collapse. The investigation is focused on the dynamic response of the stack due to an earthquake motion recorded at a nearby site. In this paper the results of a response spectrum analysis of the Tüpras stack and a generic U.S. stack are summarized. Then, a non-linear static analysis of the collapsed stack is presented using a demand-collapse comparison. The demand is represented by an acceleration-displacement response spectrum based on the recorded motion as well as some smoothed adaptations typical of design spectra, while the capacities are calculated from pushover curves using a non-linear reinforced concrete finite element analysis. Results are presented that show the effects of the hole and the orientation of the motion with respect to the hole. Also higher-mode contributions to the pushover pattern are considered. The results confirm that the stack could readily fail under the considered earthquake and are also consistent with the debris pattern.
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Size: 162 MB | Quality: 400 x 720 | Format:MKV | Year:2011 | Video Codec: MPEG-Layer 3 | Language: English
Busan, one of the busiest cities around the world was running out of room. The only solution was Geoje only 8 kms away by sea but 140 km away by road. How did the Koreans solve this problem? By building a highway immersed into the sea connecting both the cities. The Busan-Geoje fixed link. Directed and produced by Marijke De Schepper and written by Gary Parker this Nat Geo Documentary film tells the story of these two cities only 8 kilometers away by sea. One is over flowing with population while on the other one it’s hard to find a person – Busan and Geoje.
It is a four-lane highway that runs almost fifteen meters beneath the sea then leaps along two colossal cable state bridges. This was one of the biggest infrastructure projects around the world. The tunnel is composed of 18 mammoth segments each as long as two football pitches and wide enough to carry two lanes of traffic each way. Each segment was first carefully towed into the right position then aligned within 35 mm of each other.
Measures had to be taken to ensure the safety of the fixed link. Thus concrete columns were borne into the sea bed to avoid earth quakes and provide a stable ground to the highway. Later, the entire tunnel was covered with thousands of tons of crushed rock to avoid collision with ships or tankers. On the other hand, the construction of the pile on bridges was also at its peak. The bridges were huge, and the curved design was very challenging to construct. Nonetheless, the teams tirelessly kept working on the design and finally managed to complete one of the world’s toughest structures ever. How they did it and what challenges they had to face? Watch all this and much more in this Nat Geo documentary.
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