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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Size: 1.09 GB | Quality: 1280 x 720 | Format:MKV | Year:2010 | Video Codec: AC3 | Language: English
The Pearl River Tower is one of the first of a new generation of super smart buildings. It will use less than half the energy of a conventional skyscraper and will harvest the forces of nature to make energy of its own. With a curved facade that faces directly into the wind, the Pearl River Tower in China's Guangzhou City is shaped for performance. With a design specific to its environment, the Pearl River Tower utilizes a multitude of energy efficient technologies in one single structure, and symbolizes the future for super-tall building design.
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Size: 1.09 GB | Quality: 1280 x 720 | Format:MKV | Year:2008 | Video Codec: AC3 | Language: English
This case study describes what many industrial professionals said was impossible to design and build - it features the design evolution of the large scale wind turbines proposed for the Bahrain Trade Center. It gives a detailed description of the wind turbines and how they are controlled demonstrating how several innovative ideas came together were technically validated and produced the design for this unique building.
The Bahrain World Trade Center forms the focal point of a master plan to rejuvenate an existing hotel and shopping mall on a prestigious site overlooking the Arabian Gulf in the downtown central business district of Manama, Bahrain. The concept design of the Bahrain World Trade Center towers was inspired by the traditional Arabian "Wind Towers" in that the very shape of the buildings harness the unobstructed prevailing onshore breeze from the Gulf, providing a renewable source of energy for the project.
The two 50 storey sail shaped office towers taper to a height of 240m and support three 29m diameter horizontal-axis wind turbines. The towers are harmoniously integrated on top of a three story sculpted podium and basement which accommodate a new shopping center, restaurants, business centers and car parking. The full case study can be downloaded here via PDF - Harnessing Energy in Tall Buildings.
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Size: 350 MB | Quality: 352 x 480 | Format:AVI | Year:2004 | Video Codec: MPEG Layer-3 | Language: English
What began as a racing track, and thanks to Adolf Hitler’s World War II propaganda efforts, the track grew into a sophisticated high-speed road system, linking to almost all the major cities in Germany. The Autobahn boasts of having super thick road beds, 4% or less grades, wide lanes, and build on layers of technology. The Autobahn allows vehicles to travel at speeds exceeding 160km/h for roughly 2/3 of its roads. The episode profiles the operations of the highway cops, and their reliance on technology in training, monitoring of roads and various methods of arrest. It also looks at the ADAC, an automobile club, which provides on the spot road assistance. Nicknamed ‘The Yellow Angels’, they also provide air medical rescue. The system of maintenance of the Autobahn is also examined. All this infrastructure makes this mega structure into one of the world’s most safest super highway.
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Guide for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials
Reported by ACI Committee 302
This guide contains materials, design, and construction recommendations
for concrete slabs-on-ground and suspended slabs that are to receive moisture-sensitive
flooring materials. These flooring materials include sheet
rubber, epoxy coatings, vinyl composition tile, sheet vinyl, carpet, athletic
flooring, laminates, and hardwood. Chapters 1 through 8 provide an
understanding of concrete moisture behavior and drying, and show how
recommended construction practices can contribute to successful performance
of floor covering materials. This background provides a basis for
the recommendations in Chapter 9 to improve performance of floor
covering materials in contact with concrete moisture and alkalinity.
Because this guide is specific to floor moisture problems and solutions,
refer to the most current editions of both ACI 302.1R, “Guide for Concrete
Floor and Slab Construction,” and ACI 360R, “Design of Slabs-onGround,”
for general information. These two documents contain guidance
on floor design and construction that is needed to achieve successful floor
covering performance.
Keywords: admixtures; cracking; curing; curling; drying; mixture proportioning;
moisture movement; moisture test; relative humidity; slab-onground;
specifications; vapor retarder/barrier.
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