What are Expansion Joints?

Building expansion joints are expansion joints, which refers to a structural joint that is installed along the appropriate part of the building or structure to prevent cracks or damage to the structure due to changes in climate and temperature (thermal expansion and contraction). Expansion joints are used to divide building components above the foundation, such as walls, floors, and roofs (except for wooden roofs), into two separate parts, so that the building or structure can be extended horizontally in the long direction.

(1) Can be freely expanded and contracted in two directions that are parallel and perpendicular to the axis of the bridge;

(2) firm and reliable;

(3) Vehicles passing by should

It is extremely important to reasonably select the gap with the proper amount of expansion. The larger the gap, the more easily the telescopic device is damaged. The gap used is too large or too small, and the gap is adjusted without considering the temperature during installation. Especially for the plate rubber telescopic device, it is easy to cause damage. Even for continuous bridge decks, cracks often appear on the surface pavement. therefore. It is necessary to cut the bridge surface in advance, set up joints, or absorb cracks with a softer paving layer, or install small telescopic devices to solve it. In the case of large longitudinal slopes, if no structure is considered to accommodate vertical displacement, defects are also likely to occur, causing damage. The telescopic device is along the longitudinal direction of the bridge. Even if the telescopic amount is small, there is a problem that the deflection difference is large. Therefore, attention must be paid to the structure of the telescopic device. The combination of the telescopic device and the beam body into an equal strength is undoubtedly an important means to improve its use efficiency. Other types besides modular telescopic devices

Regardless of whether it is cement concrete or asphalt concrete pavement, anti-grooving construction should be adopted: reserve the slot for stakeout cut the expansion joint reserve slot adjust the expansion joint's embedded steel bar remove the slot debris install the expansion device elevation inspection Lock and tie the reinforcing bar supporting form check the pouring concrete.

1. If the pre-embedded steel bars on the beam plate are not in the correct position or have been pre-buried, you need to use the method of planting steel bars to replenish the steel bars.

2. Clean up after cutting and anchor the link.

3. Welding seams for steel bars must be sufficient, and welding must be firm.

4. The surface elevation of the concrete should be correct to prevent jumping.

5. The expansion joint is firmly anchored, does not loosen, and the expansion performance is effective.

6, the concrete maintenance time should be enough, do not open traffic because of insufficient maintenance time.

1. The construction unit is required to hoist the expansion joint in place, check whether its centerline coincides with the centerline of the beam joint, and whether its top surface is consistent with the pavement elevation, and adjust it in time. Weld the pre-buried reinforcement and expansion joint anchor firmly, and then cross 12 or 16 horizontal reinforcement. Be sure to immediately remove the expansion joint positioning pressure plate, remove the positioning screws, and use a corner grinding wheel to remove the welding scar and make up the paint. Seal the top seam of the expansion joint with adhesive tape or wooden board, and place No. 50 concrete in the notch; use a plug-in vibrator to fully compact it. Smooth the surface of the concrete transition. Use a ruler to check the top surface of the expansion joint and the transition section.

1. Inadequate design of bridge expansion joints

The beam end was not carefully considered during the design. Under repeated loading, the beam end was damaged and the telescopic device failed. In addition, the amount of deformation may not be calculated properly and an excessively large telescopic pitch may be used, which may cause damage to the telescopic device.

2. Problems with the expansion joint device itself

The structural rigidity of the telescopic device is insufficient, and the strength of the anchored component is insufficient, resulting in different degrees of damage during operation.

3. Improper selection of post-casting filling material for telescopic device

The post-casting filling material of the telescopic device is not taken seriously and carefully selected, which results in a decline in the operating quality of the telescopic device and a variety of diseases.

4.Unscientific and reasonable construction

During the construction process, the spacing of the expansion joints at the beam end was not completed according to the design requirements, artificially zoomed in and out, and the position of the positioning angle was incorrect, which caused the expansion device to fail to work properly. In this case, the following situations will occur: due to the gap being too small, the rubber expansion joint will jump due to the overrun squeeze protrusion; due to the excessive gap, the shear force under the load and the inertia of the vehicle will loosen the Expansion joint rubber brings out the positioning angle steel, creating another type of jumper. During construction, the anchoring reinforcement of the expansion device is not welded firmly enough, or the phenomenon of missing the embedded anchorage reinforcement is caused, which causes hidden dangers to the expansion joint itself; the expansion device is not installed well during construction, and the expansion joint is not well poured after the bridge deck is paved During use, expansion joints are damaged under repeated loads.

5.The continuous seam setting is not perfect

In order to reduce expansion joints, continuous beams or continuous decks are widely used. Continuous bridges need to be provided with continuous seams. The setting of continuous seams is not perfect, causing continuous seams to be damaged and causing bridge deck bouncing. At the continuous joints on the bridge deck, the width and depth of the deformed false joints are not set properly and uniformly, which also affects the normal operation of the continuous joints to varying degrees. ^[2]

1. Due to the limitation of transportation length, the telescopic device can be manufactured in sections and spliced on site. The telescopic devices stored on the construction site shall be placed in parallel and shall not be stacked in order to prevent deformation.

2. At the time of shipment, the connection clamps are provided only for convenient transportation, and the gap is not fixed. The telescopic device should be installed with the approval of the supervision engineer. If there are provisions in the design documents, the provisions in the bridge design documents shall be taken as the basis.

3. Before lifting the telescopic device in place, the concrete in the reserved tank should be shaved and cleaned. During installation, the width a of the telescopic device in the direction of the bridge should be symmetrically placed on the gap of the expansion joint, and the top level of the telescopic device should be equal to the design level, and then leveled. The anchored steel bars and the embedded steel bars on the beam are welded on both sides (as much as possible, increase the welding point and welding length to extend the service life of the telescopic device), loosen the clamp and make it freely expand and contract.

1. Galvanized sheet steel expansion joint. This is a simple expansion joint. On small and medium span assembled simple supported beam bridges, it is often used when the beam deformation is within 20-40mm.

2. Steel expansion joint. Steel expansion joints are made of steel, which can directly bear the vehicle load, and adjust the thickness of the steel cover according to the amount of expansion and contraction. Steel expansion joints are also suitable for trial use on inclined bridges. Its structure is relatively complicated, and it is only used in areas with large temperature differences or bridges with large spans. When the span is large, on the one hand, it is necessary to thicken the steel plate, on the other hand, it is necessary to use a more perfect comb-shaped steel plate expansion joint.

3. Rubber expansion joint. It uses a rubber band as the cross-stitch material. The expansion joint has the advantages of simple structure, convenient use and good effect. On large-span bridges with large deformation, expansion joints made of rubber and steel can be used. ^[1]

Expansion joints reduce impact

Under the repeated loading of the rigid abutment structure and the flexible embankment, due to factors such as artificial soil deformation or the consolidation settlement of the natural soil foundation, a large difference in settlement will cause the bridge head to trip. Bridge head jumping not only directly affects the driving comfort and increases the risk of driving. At the same time, frequent braking, braking and impact of the vehicle at the bridge head also aggravate the road surface damage on both sides of the expansion joint. Therefore, solving bridgehead jumping has always been a very important problem in highway design.

Expansion joint improvement ideas

There are many ways to deal with bridgehead jumps, such as: changing materials behind the platform, preloading early, composite foundation, geogrid, reinforced abutment, etc., and the most common practice is to set up bridgeheads. Hebei Province has basically adopted all of them. Bridgehead planking disposal plan.

In recent years, the structure description of bridgehead slabs and elastic joints has followed a traditional practice, that is, setting up elastic equipment between the main beam and the back wall of the abutment, and placing the bridgehead slab on the corbel behind the back wall. A structural joint is formed between the slab and the back wall of the abutment. Practical engineering inquiry has proved that this type of structure is not ambitious in its application and cannot be used to handle bridgehead jumps. It is necessary to improve it.

Problems with expansion joints

1. There is a rigid joint running through between the back wall of the abutment and the end of the slab. Although it is implored that asphalt batt be filled in the joint as water-proof material during construction, due to the expansion and contraction of the joint in practice Deformation and slab end change easily cause damage to the asphalt concrete pavement. As a result of this damage, the pavement cracks, and the surface water directly erodes the backfill of the platform along the joints, causing the backfill to softly deform or lose emptying, which causes the subgrade to settle there, and it appears empty under the slab.

2. The settlement of the tail end of the slab will make the front corner and vertical displacement, and make the height difference between the two ends of the joint. Because the gap between the seam and the elastic seam is very short, the car will jump twice in rapid succession when it comes to the end. The larger the span, the higher the fill, and the longer the plank, the more pronounced the jump will be, and the oscillation will occur. It will be bigger.

3. Repeated braking, braking and bumping of the car at the bridge head increase the damage of the road surface and the telescopic device on the seam side.

Solving the above problems can reduce the impact of expansion joints and the disadvantages of bridgehead slabs, achieve long-term use of expansion joints, and reduce the number of replacements.