In the construction of segmental bridges using the short-line match casting method, alignment control during the precasting stage serves as the foundation for ensuring that the as-built bridge alignment meets the design requirements. However, due to factors such as precasting measurement errors, match-cast surface machining accuracy, temperature deformation, and concrete shrinkage and creep, deviations inevitably occur during the precasting alignment control process. Such deviations cannot be eliminated during the precasting stage and must be corrected during the erection stage. The preceding article systematically expounded the establishment of the survey control system during the erection stage, the precise positioning methods for pier top blocks and starting segments, and the sequential erection process for the remaining segments. Building upon this foundation, this paper further explores the error adjustment measures that can be adopted when deviations occur in the erection alignment, thereby providing comprehensive technical support for high-precision assembly in short-line match cast segmental bridges. 

The alignment adjustment measures during segmental erection are as follows: adjusting the tensioning sequence and tensioning force of the internal prestressing tendons (with appropriate over-tensioning), applying counterweights appropriately, adjusting the tensioning sequence and tensioning force of temporary prestressing tendons, adding epoxy resin shims at the joints between adjacent segments, varying the application thickness of epoxy resin adhesive, and grinding the segment end faces. When the balanced cantilever erection method is adopted, all the above measures are effective. However, due to the constraints of its construction process, the span-by-span erection method has limited adjustment measures and a narrow adjustment range.

1. Adjusting the Tensioning Sequence and Force of Internal Prestressing Tendons

This method is applicable only to the balanced cantilever erection method. During cantilever erection, tensioning is generally performed in a left-right symmetrical sequence and from top to bottom. If alignment correction is required during construction, the prestressing tensioning sequence and force may be appropriately adjusted. The specific methods are as follows: (1) After dry match test fitting, if axis deviation to the right is observed, tension the left-side internal prestressing tendons first, followed by the right-side internal prestressing tendons. After all internal prestressing tendons are tensioned, apply moderate over-tensioning to the left-side internal prestressing tendons. If the deviation is to the left, the opposite applies. (2) After dry match test fitting, if the elevation is found to be too high, tension the internal prestressing tendons in the bottom slab first, followed by those in the top slab. After all internal prestressing tendons are tensioned, apply moderate over-tensioning to the internal prestressing tendons in the bottom slab. If the elevation is too low, the opposite applies.

When using this method for alignment adjustment, the prestressing tensioning sequence must be altered, and the tensioning force must be moderately adjusted. Theoretical analysis shall be conducted prior to application to determine its feasibility.

2. Adjusting the Tensioning Sequence and Force of Temporary Prestressing Tendons

When the span-by-span erection method is adopted, the internal and external prestressing tendons are tensioned only after the entire span of the main girder is closed. Therefore, adjusting the tensioning sequence and force of internal prestressing tendons is ineffective for this method. However, practice has shown that alignment can also be adjusted by modifying the tensioning sequence and force of temporary prestressing tendons. The specific methods are as follows: (1) After dry match test fitting, if axis deviation to the right is observed, tension the left-side temporary prestressing tie rods first, followed by the right-side temporary prestressing tie rods. After all temporary tie rods are tensioned, apply over-tensioning to the left-side temporary tie rods, ensuring that the over-tensioning force does not exceed the allowable capacity of the temporary tie rods. If the deviation is to the left, the opposite applies. (2) After dry match test fitting, if the elevation is found to be too high, tension the temporary prestressing tie rods in the bottom slab first, followed by those in the top slab. After all temporary tie rods are tensioned, apply over-tensioning to the temporary tie rods in the bottom slab, ensuring that the over-tensioning force does not exceed the allowable capacity of the temporary tie rods. If the elevation is too low, the opposite applies.

Practice has verified that adjusting the tensioning sequence and force of temporary prestressing tendons can fine-tune the erection alignment, with a maximum fine-tuning range of approximately 3 mm.

3. Adding Epoxy Resin Shims at Joints Between Adjacent Segments

Epoxy resin shims are made of the same material as the epoxy adhesive. The shim dimensions are 15 cm × 15 cm, with a typical thickness of 3–4 mm. Two shims are placed per cross-section at the intersections of the box girder webs with the top slab and bottom slab (where the concrete is thickest). The shims shall be arranged in a left-right symmetrical or top-bottom symmetrical pattern. During placement, care shall be taken to avoid the ducts for internal prestressing tendons, and the adhesive thickness on the concrete surface on the shim side shall be increased to ensure that the extruded epoxy adhesive is dense after assembly. The specific methods for adjusting erection alignment by adding shims are as follows: (1) After dry match test fitting, if axis deviation to the right is observed, place two shims arranged symmetrically from top to bottom on the right side and increase the epoxy adhesive thickness on the right side. If the deviation is to the left, the opposite applies. (2) After dry match test fitting, if the elevation is found to be too high, place two shims arranged symmetrically from left to right on the top slab and increase the epoxy adhesive thickness on the top slab side. If the elevation is too low, the opposite applies.

This method has been applied in the construction of many similar bridges, achieving significant results with a maximum fine-tuning range of approximately 5 mm.

4. Varying the Application Thickness of Epoxy Resin Adhesive

Varying the epoxy adhesive thickness is similar to adding epoxy shims, as both methods achieve erection alignment error adjustment by creating non-uniform adhesive joint thickness. First, a layer of epoxy adhesive is applied to the match-cast surface of the segment to be erected, with a slightly thicker application on the side toward the alignment deviation direction and a thinner application or no application on the opposite side. After the epoxy adhesive achieves initial setting, the adhesive is uniformly applied across the entire cross-section, and the segment is erected. Since the initial setting time of epoxy adhesive is ≥ 2 hours, and is even longer in winter when temperatures are low, this method may affect the construction schedule and continuity. Therefore, it is generally applied only when the erection alignment error is significant.

5. Grinding the Segment End Faces

This method corrects alignment errors by altering the thickness of the box girder. The entire end face of the segment must be ground, and the grinding thickness shall be determined after accurate calculation. The ground surface must be flat. Due to the presence of numerous shear keys and shear key slots, this method is difficult to implement, and the joints during the erection stage are not easily closed.

6. Applying Counterweights Appropriately

This method is applicable only for elevation deviation adjustment in the balanced cantilever erection method. If one side of the T-structure settles while the other side rises during erection, counterweights may be appropriately added on the rising side after completing the T-structure construction to correct the elevation deviation. Adjusting elevation errors through counterweights yields significant results. However, before applying counterweights, a systematic assessment of the anchorage system of the pier top block and the stress state of the entire T-structure must be conducted to ensure construction safety.

Conclusion

In summary, error adjustment methods during the erection stage shall be selected based on the magnitude of the deviation, with dry match test fitting as a prerequisite. By comprehensively applying measures such as prestressing adjustment, shim addition, adhesive joint modification, and grinding, a systematic and flexible deviation correction mechanism is established, ensuring that the erection alignment of short-line match cast segmental bridges meets the design requirements.