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Shear and moment diagram part 1

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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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The reasons behind the trimming of pile head

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In general, the bored piles are casted to a level higher than the required pile cut-off level. Pile cut-off level is usually similar or a little bit higher than the blinding level of a pile cap. the process of constructing a cast-in-situ pile involves the following steps: installation of the temporary casing to prevent the soil collapse during the drilling process and to guide the drilling rig. Drilling the pile to the required level and diameter. Installation of a reinforcement cage. Reinforcement cage vertical bars will be extended above the pile cut-off level to improve the bonding with the pile cap. The casting of concrete usually done with a tremie pipe. Tremie pipe will be lowered to the bottom of the pile, and then the concrete will be poured. Once the casting is completed, the temporary casing will be removed. It is a common practice to cast the concrete above the cut-off level. the concrete casted then removed for the following reasons: during the casting pro...
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shear key

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The purpose of the shear key is to improve the bonding between concrete surfaces. The shear key is usually made at the construction joint location to enhance the adhesion between the old and new casted concrete. Construction joint is considered a weak point because the concrete is not casted at one time, in large structures where the concrete can not be casted for some members at one time, such as a slab. We usually divide the slab and cast it at many stages. The large quantities of concrete will make it impossible to cast the slab at one time. Therefore, the casting will be done in several stages. The location of the construction joint should be selected carefully. Construction joint shall be made at the location of minimum shear and moment.  The bonding between old and new concrete can be improved by roughening the old concrete and forming a shear key on the concrete surface while the concrete is still plastic. The shear key can be formed by pressing timber into the concrete surf...
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Bundled Bars

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sometimes the required reinforcement bar will not fit for a given section of beam or girder, in this case, we resort to bundling a group of parallel bars, up to four bars can be bundled together,  ACI 7.6.6.2 stating that bundled bars should be enclosed within stirrups or ties, bundled bars should be tied, wired and fastened together to ensure remaining in position whether vertical or horizontal, ACI 7.6.6.3 stating that bars have diameter greater than 36 mm(#11) shall not be bundled in beams, the limitation of bundled bars size is for beam or girders in building, the small size of building members make it unpractical to bundle bars with size larger than 36mm(#11), in bridges the size of members are bigger and therefore it is allowed to bundle up to two bars with size greater than 36mm (#11). figure 1 showing bundle bar arrangements. figure 1 construction management: concrete construction bridge construction:How to become a bridge engineer when two or more ...
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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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why do we stagger reinforcement overlapping?

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First, we should know that steel rebar comes in standard length such as 12m. using very long reinforcement is impractical because it will result in difficulties in handling reinforcement by steel fabricators. Also, longer rebar is heavier and difficult to lift and move. So for a long structure such as a slab, we require a reinforcement length that is more than the standard reinforcement. We can't use a single piece of rebar for a specific length for such a structure, so we use two or more steel rebars to cover the entire length of the structure. Figure no:1 The zone of overlapping between reinforcement will be considered as a weak zone. Therefore, it is a good practice to stagger the reinforcement overlapping. Staggering is done by overlapping the reinforcement at a different location. Staggering reinforcement overlapping will reduce the number of rebars overlapped at the same point, which will be beneficial in two ways. Firstly, it will reduce the discontinuity of rebar at the s...
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Chamfers for concrete structures

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In general, the edges of concrete members are chamfered. Usually during the process of installing forms for a structural member such as pile cap, a chamfer a PVC chamfer as shown in figure no:1 installed at the edges of the structural members. These chamfers will form smooth slanted edges, as shown in figure no:2. The size of chamfers can be 20x20mm or more as shown on the contract drawing. The PVC chamfer fixed to forms by nails. We should ensure that the PVC chamfer fixed in their correct locations, and we should ensure that the PVC chamfer is straight and not moving up or down. Checking the alignment and location of PVC chamfer is important, so the chamfered concrete edge will have a good appearance after the form’s removal.  Figure 1 Figure 2 Chamfering the concrete edges done for many reasons such as aesthetics, some suggesting that the chamfering of concrete edges done for safety to reduce the damage of objects due to impact with sharp concrete edges. Actually, ...
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Face dowels (ground improvement for tunnel excavation)

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Fiberglass dowels are used widely to stabilize the poor ground for excavating tunnels. Face dowels are installed over the cross-section of the tunnel. Fiberglass reinforcement can be used to reinforce the excavated area. Fiberglass dowels installed in predrilled holes then injected with cement mortar. Dowels used to strengthen the face of the tunnel should be made from a material that can be easily excavated. Fiberglass reinforcement can be excavated easily. Using of fiberglass reinforcement will be suitable when TBM or road header used to excavate the tunnel as they can be easily excavated and removed. However, the using of fiberglass dowels for other methods of excavation may pose a risk because fiberglass is a brittle material. The breaking of fiberglass will produce potentially dangerous sharp edges, which may affect the safety of workers. Figure 1 construction management: concrete construction bridge construction:How to become a bridge engineer Steel d...
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wing wall arrangement and orientation for abutments

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wing wall main function is to retain the embankment near abutment. the common slope is 2:1. greater than 2:1 is not allowed. figure no: shows a wing wall for the abutment. Figure 1  there is three arrangement for wing wall: wing wall parallel to abutment: easy to build. construction can be done in a short time. this type of wing wall will not disturb the existing embankment and utilities but it is not the most economical arrangement.   figure 2 construction management: concrete construction bridge construction:How to become a bridge engineer wing wall at an angle with abutments: this type is most economical among the three arrangement. Figure 3 wing wall perpendicular to abutment: in this arrangement. wing wall provides a continuous alignment with bridge deck which can be used to support parapets. this arrangement will disturb existing embankment and utilities adjacent to the structure. for curve bridge, this type o...
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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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