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prestressing equipment

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Jacks are essential tools in prestressing operations and are used to apply tension to strands within tendons. There are two main types of jacks: A. Mono-Strand Jack A mono-strand jack is primarily used in building construction, where tendons typically consist of a small number of strands (usually 3 to 4). This type of jack is designed to stress each strand individually, ensuring precise control over the tensioning process. Since buildings generally have shorter tendons compared to bridges, stressing strands one by one is a practical and efficient approach in this context. construction management: concrete construction bridge construction:How to become a bridge engineer B. Multi strands jack:  In bridge construction, where tendons contain a significantly larger number of strands, using a mono-strand jack would be impractical. Stressing strands one by one in such cases would not only be time-consuming but also increase the risk of strand entrapment. Ther...
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Impact of Hot Weather on Concrete and Necessary Precautions

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Concrete placement should not be permitted if the ambient temperature exceeds 38°C to 40°C . hence, it is recommended to place concrete when temperature is less than 35°C . If the temperature reaches 35°C or more, special precautions must be taken, as hot weather accelerates water evaporation from the concrete. This rapid evaporation negatively affects the hydration process, leading to reduced concrete strength and durability. Adverse Effects of Hot Weather on Concrete Increased Shrinkage – high temperatures cause excessive moisture loss, leading to greater shrinkage in concrete. Higher Risk of Cracking – Rapid drying can induce thermal and plastic shrinkage cracks. Reduced Durability – Increased evaporation increase concrete porosity, compromising its long-term strength and resistance to environmental factors. construction management: concrete construction bridge construction:How to become a bridge engineer Special Measures to Mitigate Hot Weather Effects To minimize ...
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Hardware for post-tensioning

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1. Anchorage Anchorage is a device used to secure prestressing steel and is installed at the edge of a concrete member or the prestressing end. There are two main types of anchorage: Dead-end anchorage : Embedded within the concrete, providing a fixed termination point for the prestressing tendons. Live-end anchorage : Positioned at the edge of the concrete member, where prestressing occurs. The jacking operation is done at the live end anchorage and the applied load is transferred to concrete members after the completion of tendon jacking. construction management: concrete construction bridge construction:How to become a bridge engineer Anchorage device consists of: anchorage device A. Bearing plate :  Typically round or rectangular, its primary function is to transfer the prestressing force from the tendons to the concrete. bearing plate and wedging plate B. Wedging plate:  This component holds the stra...
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Axle Load Surveys: Importance, Methodology, and Best Practices

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Axle load surveys , play a crucial role in determining the pavement actual loads and this will impact a new road design and maintenance in future. These surveys provide essential data for cost-effective pavement design and for the preservation of existing roads . However, axle load surveys can be costly, requiring careful planning and execution to ensure accuracy and efficiency. Axle load surveys help in the accurate calculation of Equivalent Axle Load Factors (EALF) and Truck Factors (TF) . These parameters vary based on axle configuration and axle loads. They are used, along with other factors, to determine the Equivalent Single Axle Load (ESAL) which is  a representative value that quantifies traffic loads on pavement, forming the basis for pavement design. Vehicle Classification in Axle Load Surveys Different types of vehicles contribute differently to pavement deterioration. It is important to categorize vehicles properly to ensure that the survey results are relevant and re...
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Pre-tensioning and Post-tensioning in Prestressed Concrete

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Pre-tensioning In pre-tensioning, the prestressing reinforcement (strands or bars) are tensioned before the casting of concrete. Once the concrete gains sufficient strength, the prestressing force is transferred from the tendons to the concrete. Stages of Pre-tensioning: Tendon Placement & Tensioning High-strength steel strands are stretched between two end abutments (bulkheads) within a prestressing bed. Concrete Casting Concrete is cast around the tensioned tendons and left to cure. Transfer of Prestress After the concrete attains the required strength, the tendons are cut loose from the abutments. The prestress is transferred to the concrete due to the bond between the tendons and the hardened concrete. Effects of Prestressing The concrete undergoes elastic shortening due to the prestressing force. If tendons are placed eccentrically, the member develops a camber (upward deflection). Post-tensioning In post-tensioning, concrete is cast first , and after it gain...
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Pile cap

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Pile cap used to transfer the loads from superstructure to the piling. The pile cap is thick concrete mat rests on piles. It is part of the foundation and used to distribute the loads over the piles. Piles used when the soil bearing is not enough to carry loads of the structure. Figure 1  construction management: concrete construction bridge construction:How to become a bridge engineer Pile cap construction procedure Excavation around piles: After 7 days of the casting of the pile the concrete will gain approximately, 70% of it is compressive strength. The soil around piles will be removed to the required levels and dimension that allows construction of the pile cap. A step shall be made if the excavation is more than 1.5 m to prevent soil collapse. Figure 2 Pile head cutting: Concrete will be removed up to cut off level. If concrete under the cut off level is unsound. It shall be removed, and the pile will be repaired...
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Binding wire for steel reinforcement

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  Binding wires are used to tie steel bars together. These wires are playing a significant role in maintaining the reinforcement stability and rigidity. Wires are used to tie the steel bars at intersections points. By tying the steel bars together, we ensure that the steel bars will not move from their locations during construction or during the time of concreting. In slabs, binding wires are used to tie longitudinal and transverse bars together. In columns, it is used to tie vertical bars with stirrups.   Figure 1 There are various types of binding wires such as  Black annealed baling wire, Stainless Steel Binding Wire, and PVC coated binding wires.  Black annealed baling wire used to tie black steel. The popular size for black wire ranges from 16 to 22 gauges. Stainless steel binding wires are used to bind stainless steel reinforcement. Stainless steel reinforcement is used in a harsh environment where the black steel gets rusted quickly. Therefore, stainless ...
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Bar Bending schedule (BBS)

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 The bar  bending schedule is a table that contains the details of reinforcement for a specific structural member such as footing, column, slab, and others. The bar bending schedule will contain the bars' dimensions to be used, the shape of the bars, the size of bars, bar mark, number of bars, and the weight of bars. BBS will be used to determine the weight of reinforcement required for a specific structural member.  there are various advantages of bar bending schedule such as: estimating the quantity of reinforcement for each structural member. So we can estimate the amount of reinforcement required for a construction project.  BBS will help in reducing the losses of steel by procuring the precise quantity of different rebar diameter.  BBS will reduce the wastage of reinforcement by providing the engineers with the exact dimension and shape of rebars. Knowing the exact dimension and shape will reduce the time of cutting and bending rebars.  BBS will reduce...
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Bridge Diaphragm

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The main function of diaphragms is to provide a stiffening effect to deck slab in case bridge webs are not situated directly on top of bearings. Therefore, diaphragms may not be necessary in case bridge bearings are placed directly under the webs because loads in bridge decks can be directly transferred to the bearings.On the other hand, diaphragms also help to improve the load-sharing characteristics of bridges. Diaphragms also contribute to the provision of torsional restraint to the bridge deck. Diaphragm will be used also to resist stresses that occurs during the post-tensioning process. Post-tensioning hardware are casted inside the diaphragm. Figure 1 construction management: concrete construction bridge construction:How to become a bridge engineer Types of diaphragm: Diaphragm at the span end: this type of diaphragms will be located between two bridge spans or at the bridge abutments. Expansion joints will be used to connect bridge spans. This ...
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stress-strain diagram for aluminium alloy and rubber

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figure no:1 showing the stress-strain diagram for aluminum alloy. we can notice from the stress-stress diagram that aluminum has a considerable ductility. despite the absence of explicit yield point as in structural steel . the initial portion of the stress-strain curve is linear with a recognizable proportional limit. the proportional limit for aluminum alloy ranges from 70 to 410 Mpa (10 to 60 Ksi). aluminum alloy undergoes large strain before failure. ultimate stress ranges from 140 to 550 Mpa (20 to 80 Ksi). construction management: concrete construction bridge construction:How to become a bridge engineer Figure-1 Yield stress for aluminum alloy can be determined by drawing offset line parrel to the linear portion of the stress-strain curve. the straight line offset by a standard strain such as 0.002. the intersection point with the stress-strain curve is the point of yield stress. figure no:2 illustrates the concept of offset method. yield stress acquire...
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Non-Working Pile Testing and Static Compression Load Test

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Purpose of Non-Working Piles Non-working piles are constructed at the beginning of the project to evaluate soil bearing capacity and determine the maximum settlement. These piles are loaded up to twice the working load. Based on the test results, the pile length may be adjusted. If the measured settlement exceeds the allowable limit, the pile length will be increased accordingly. construction management: concrete construction bridge construction:How to become a bridge engineer Static Compression Load Test The static compression load test provides insight into how the pile responds to loading. Settlement is measured at different load increments to determine the appropriate pile design length. The maximum applied load is typically twice the working load (2 × working load) or as specified by local standards. The following steps outline the testing procedure: A. Steel Cage Preparation The steel reinforcement cage is prepared in accordance with the approved shop drawings. ...
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Repairing of concrete bulging

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Improper designing and installation of formwork for a concrete member can result in concrete Bulging. During the placing and compacting of concrete, forms may deflect largely in the weak areas. The deflection of forms will cause concrete to expand at this location, and this known as concrete Bulging. Concrete Bulging will spoil the appearance of a concrete member. Therefore we should always ensure that the forms are appropriately installed, and it is sufficiently supported to resist the concrete during placing and compacting. Bulging should be repaired in case we couldn't avoid it. The solution of concrete Bulging, offset, or surface irregularities are surface grinding. However, excessive surface grinding can weaken the concrete.  Figure 1 If the bulging or surface irregularities are small, grinding of concrete surface will be sufficient to remove surface irregularities. If the Bulging of concrete is significant, then the concrete should be chipped, and the surface...
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Prestressing stands debonding

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  Prestressing bridge concrete beams contributes to resisting the tensile stresses caused by the traffic loads and the beam's weight. Stressing concrete has various benefits, such as increasing concrete members' capacity, reducing the concrete member section, and increasing the span lengths for structures such as bridges and buildings. However,  The stressing of bridge beam ends can result in unwanted cracks. Therefore AASHTO calling for debonding a specific portion of strands at the beam end to minimize the stresses and reduce cracks. Figure 1 Debonding is achieved by wrapping the strands at the end of the beam with plastic. Wrapping the strand with plastic wrapping will prevent the strands from bonding with concrete, thus avoid transferring unwanted stress to the beam end. As a result, the unwanted cracks will be prevented by reducing the stress levels at the end of the beam.  
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Determinate and indeterminate structure

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structure can be called determinate if the equilibrium equation provides enough and sufficient condition for equilibrium. if all forces for a structure can be determined using equilibrium equations only, this structure is determinate, but if the unknown forces are more and cant be determined using equilibrium equations then this structure is indeterminate.in general we can determine if a structure is statically determinate or indeterminate by drawing free body diagram for a structure or part of it and comparing a number of unknown forces and moment component with number of available equation of equilibrium. for coplanar structures, we have  three equilibrium equations, if n is the total number of parts and r is the number of unknown forces and moment component then: r=3*n determinate r>3*n indeterminate  construction management: concrete construction bridge construction:How to become a bridge engineer statically indeterminate structure cant ...
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Concrete repair-selecting the repair method

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Repairing concrete structure passes through various stages. Selecting the correct repair method will depend on completing the previous steps, such as determining the cause of concrete damage, evaluate the extent of the damage, and assess the need for repair. The completion of these steps will define the type of conditions the repair must resist, the available repair construction time period, and when repairs must be accomplished. The data collected from performing these steps will help in selecting which of the 15 standard methods is suitable and durable for repairing the damaged concrete structure. Figure 1 In general, the old concrete surface should be prepared before beginning with the repairing process. It is essential to remove all unsound concrete before applying the repairing. Improper preparing of damaged concrete structure will result in unsatisfactory repair with low durability. The first step in preparing the old concrete surface is the saw cutting of repairin...
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