Beam Modification Plan for Prefabricated Slab Houses

The modification of beams in prefabricated slab houses requires following scientific steps to ensure structural safety and construction quality. The specific plan is as follows:

I. Preliminary Preparation and Measurement Positioning

1. Structural Inspection and Appraisal: Before construction, a professional agency should be commissioned to conduct a structural inspection of the house, verify the load-bearing capacity of the original load-bearing walls, and assess whether wall or foundation reinforcement is required. If the original structure shows signs of aging or damage, priority should be given to repair.
2. Measurement Positioning: Based on design requirements, accurately measure the target load-bearing wall to determine the position, span, and cross-sectional dimensions (such as height and width) of the new beam. Draw detailed construction drawings that specify parameters such as steel reinforcement configuration and concrete strength.

II. Demolition and Support System Construction

1. Wall Demolition: Demolish the original load-bearing wall to the design elevation (usually the beam bottom height), clean up the concrete debris, and sort and recycle reusable materials. Avoid causing impact to surrounding structures during demolition.
2. Support Steel Frame Installation: Install a temporary support steel frame below the demolition area. Its specifications should be determined based on the beam span and load calculations. The steel frame should be fixed with bolts or welding to ensure stability and prevent structural deformation during construction.

III. Steel Reinforcement Binding and Formwork Installation

1. Steel Reinforcement Configuration:
   • Bind the bottom reinforcement, secondary reinforcement, and stirrups of the beam. Control the stirrup spacing according to design requirements (usually 5 to 7 per meter) to ensure the shear resistance of the steel reinforcement skeleton.
   • The steel reinforcement should be reliably welded or bound to the embedded reinforcement or connectors of the original structure to form an integrated load-bearing system.
2. Formwork Installation:
   • The side formwork can be installed using a combination of vertical and inclined methods or through formwork opening for grouting. The formwork should be firmly reinforced to prevent bulging during concrete pouring.
   • For prefabricated slab houses, special attention should be paid to sealing the formwork at the connection between the floor slab and the beam to prevent grout leakage.

IV. Concrete Pouring and Curing

1. Pouring Method:
   • Side Formwork Grouting: Pour concrete in layers through openings at the edge of the formwork using a small conveyor. Each layer should not exceed 30 cm in thickness and should be vibrated densely.
   • Opening Grouting: Remove or break part of the floor slab in the prefabricated slab area and pour concrete through the openings. For long beams, openings should be made at intervals (e.g., every 1.5 meters) to ensure that the concrete fills without voids.
2. Curing Requirements:
   • The side formwork can be removed 24 hours after pouring. The bottom formwork and supports should have their curing time adjusted according to the season (at least 15 days in summer and at least 20 days in winter), with continuous watering to keep them moist during this period.
   • The bottom formwork and supports can only be removed after the concrete strength reaches 100% of the design value (usually 28 days).

V. Reinforcement Treatment and Acceptance

1. Reinforcement Measures: After construction, apply waterproof and fireproof coatings to the beam surface. If necessary, add sound insulation materials. Check the connection nodes between the beam and the original structure to ensure there are no cracks or looseness.
2. Acceptance Criteria: Check the beam's dimensional deviations, steel reinforcement cover thickness, and concrete strength in accordance with the "Code for Acceptance of Construction Quality of Concrete Structures". Only after passing the inspection can the beam be put into use.

Precautions: Beam modification projects involve structural safety and must be carried out by a qualified team. Unauthorized modifications are strictly prohibited. During construction, the house's settlement and cracks should be continuously monitored, and any abnormalities should be dealt with promptly.