In bridge engineering, expansion joints are required to be capable of freely expanding and contracting in both directions parallel and perpendicular to the bridge axis, being firmly reliable, smooth without sudden jumps or noise when vehicles pass over, able to prevent rainwater and debris from infiltrating and clogging, and easy to install, inspect, maintain, and remove contaminants. At the location where expansion joints are set, the railings and bridge deck pavement should be disconnected. What are the construction methods for bridge expansion joints? Let's dive in.

The Role of Bridge Expansion Joints

Bridges experience displacement due to dynamic loads, temperature, concrete shrinkage, and creep, and excessive displacements can affect driving comfort and safety. To adjust the displacements and connections between the upper structures of bridges, expansion joints must be set.

Types of Bridge Expansion Joints

Bridge expansion joints are classified into the following five categories:

Steel-supported type, combined shear type (plate type), modulus-supported type, butt joint type, and seamless type expansion joints.

Construction Method of Bridge Expansion Joint

Expansion joints can be damaged, subsided, or misaligned, causing impact shock to bridges when vehicles pass over them, increasing loads and potentially causing safety accidents. To eliminate phenomena such as steps and bumping, the installation of bridge expansion joints is a crucial project, and construction defects cannot be ignored.

1.Construction Preparation

Before construction, be familiar with the relevant construction drawings and the operating procedures for expansion joint installation, and check the flatness, straightness, and joint gap of the special-shaped side beams. According to the actual situation of the project, it is necessary to be equipped with sufficient mechanical equipment and small machines and tools, and the springboards must be of solid quality so that the passing construction vehicles to pass smoothly. At the same time, be fully equipped with canvas, plastic cloth and plastic film, straw mat, etc. for conservation to ensure the smooth progress of construction.

2.Cutting Joints

Before construction, according to the construction design drawing for lofting by using a cutting machine to cut the joints, pay attention to protecting the pavement outside the cutting line to prevent pollution, and ensure the integrity of the cutting joint incision.

3.Slotting

Use a pneumatic pick to slot, and the concrete and sundries in the groove should be removed cleanly, especially the sundries in the gap at the beam end, and straighten and adjust the embedded bars in the groove. If the number of embedded bars is found to be insufficient, expansion bolts should be driven and the embedded bars should be replenished. And invite the owner's representative and the supervisor to jointly accept and inspect to ensure the quality of the expansion joint.

4.Installation

4.1 Before installing the expansion device, check the anchoring width of the embedded bars of the expansion joint. Generally, it is appropriate to set it at about 50 cm. It is appropriate to adopt the width of the back wall on the bridge abutment, which not only strengthens the stability of the expansion joint device, but also facilitates the construction of the bridge deck; use a high-pressure water gun to remove the sundries in the expansion joint groove and check whether it is clean. Check the flatness of the profile steel. During the installation process, detect the straightness and flatness of the expansion joint profile steel. The flatness is controlled within 2mm, the straightness is controlled within 3mm, and the height difference between the top surface and the pavement is controlled within 2mm.

4.2 When installing and fixing, use a gantry hanger and 10*10 angle steel as the positioning angle steel. The center line of the expansion joint coincides with the center line of the beam end, and the top surface of the expansion joint is lower than the elevation of the asphalt concrete pavement (1-2mm). Before temporarily fixing and spot welding, adjust the elevation and straightness to meet the design requirements before proceeding. To fix, weld one solder joint for every 2-3 anchor bars from one side of the bridge width to the other side in a sequence. To prevent the expansion joint does not shift, weld symmetrically from both sides. It is strictly prohibited to weld from one end to the other end.

4.3 After fixing, re-measure the elevation of the expansion joint once again. After confirming that there is no deformation or deviation, weld the anchor bars and the embedded bars firmly on both sides at the same time and weld them all at once. If it is difficult to weld when welding on one side, you can weld on the other side first, and then weld on the left, middle and right positions. When the workload of single-side welding is large and the time is long, and the influence of temperature difference changes is large, after single-side welding is good, the other side can be welded at the same time, and pay attention to the distance between the solder joint and the profile steel to ensure that the profile steel does not deform. In order to prevent the phenomenon of bumping cars, according to the specification requirements, the flatness of the profile steel should be controlled within the range of 0-2mm. After the expansion joint is firmly welded, remove the temporary fixing clamps, positioning angle steel, etc. to make it freely expand and contract.

4.4 Formwork generally use foam boards, fiberboards, thin iron sheets, etc., and the installation must be firmly and tightly to ensure that there is no movement when the concrete is vibrated to prevent mortar from flowing into the joint and affecting the use of the expansion joint. Lay steel mesh 3mm lower than the pavement elevation on both sides.

Pouring concrete

Before pouring, plastic cloth should be spread on both sides of the joint to avoid concrete contaminating the pavement. The slump of the concrete should be <2cm. In order to reduce the water-cement ratio and improve the early strength, admixtures can be added to reduce the surface shrinkage of the concrete. After the concrete is compacted by vibration, use a trowel to bring out the cement slurry and smooth it with 4 to 5 times. Strictly control the flatness of the concrete surface to make it flush with the top surface of the expansion joint device.

Maintenance

Before the concrete reaches the initial set, use a brush to roughen the surface, cover it with plastic sheeting, and keep it moist by watering. Maintain a moist surface for a curing period of not less than 7 days. During this period, prohibit vehicle passage. Only after the strength reaches at least 50% of the designed strength can rubber sealing strips be installed.

 To Wrap Up

This article introduces the role, classification, and construction methods of bridge expansion joints. By detailing the precautions and requirements of each link in the construction process, it emphasizes the importance and technical points of expansion joint construction. If you want to know more about the problems and prevention measures of bridge expansion joints, please stay tunned to us.