The Foundation of Steel Structure Engineering: A Comprehensive Guide to Independent Foundation Construction Steps
Before a grand steel structure building rises from the ground, the first and most crucial step is to create a solid and reliable "foundation" for it – the independent foundation. It acts like the "feet" of the structure, safely transferring all the loads from the superstructure to the ground. Today, we will delve into the entire construction process of an independent foundation for steel structure engineering, exploring the precision engineering hidden beneath the soil.
Step 1: Precise Excavation of the Foundation Pit
The initial step involves earth excavation. This is not merely "digging a hole" but a precise operation.
Size Determination: The dimensions (length, width, depth) of the foundation pit are not arbitrarily set. They are determined through precise calculations by professional engineers based on the loads transmitted from the steel column and the bearing capacity of the soil. The basic principle is: the greater the load from above, the larger the required base area, and consequently, the wider and deeper the foundation pit.
Setting Out and Positioning: Before excavation, surveyors use instruments like total stations for precise setting out, marking the exact location and boundaries of the pit with lime or stakes, ensuring complete alignment with the design drawings.
Pit Bottom Preparation: After excavating to the designed elevation, the bottom must be leveled and compacted to ensure the subsoil is firm and even, providing a good base for subsequent work.
Step 2: Placing the Blinding Concrete and Reinforcement
Once the pit is formed, we begin building its "skeleton."
Pouring Blinding Concrete: A layer of plain concrete blinding is typically poured onto the compacted pit bottom. This layer primarily serves to level, seal against water, and create a solid working surface for subsequent rebar work.
Tying Foundation Base Slab Reinforcement: According to the structural drawings, a reinforcement mesh is placed and tied on the blinding. These rebars form the "skeleton" of the foundation, mainly resisting bending moments and tension. Their specifications, spacing, and lap lengths must strictly adhere to design codes.
Embedding Short Column Reinforcement: While tying the base slab reinforcement, the vertical rebars for the upper short column (or "foundation neck") are accurately fixed to the base slab reinforcement, ensuring they will bond firmly with the short column concrete later.
Step 3: Pouring the Foundation Base Slab Concrete
With the "skeleton" in place, we begin "filling the flesh" – pouring concrete.
Concrete, mixed according to the specified design mix ratio, is poured into the erected formwork, completely covering the rebar mesh.
During pouring, vibrators are used thoroughly to eliminate air bubbles, ensuring the concrete is dense and uniform, free from defects like honeycombing.
After pouring, the surface is finished smooth, then covered and moist-cured to ensure steady strength gain.
Step 4: Precisely Fixing the Anchor Bolts
This is one of the most critical and accuracy-intensive steps in steel structure foundation work.
Positioning and Alignment: Anchor bolts are the "joints" connecting the steel column to the foundation. During construction, a precise positioning template (steel plate or section) is first used to hold a set of anchor bolts together. Then, total stations or theodolites are used for precise positioning and level alignment.
Securing Fixation: After ensuring their planar position and verticality are controlled within millimeter tolerances, the bottom ends of the anchor bolts are welded securely to the foundation reinforcement to prevent displacement or tilting during subsequent concrete pouring.
Step 5: Formwork and Pouring of the Short Column Concrete
Once the anchor bolts are secured, construction of the short column on top of the base begins.
Erecting Formwork: Formwork is erected around the foundation base slab to shape the short column.
Pouring Concrete: Concrete for the short column is poured. Care must be taken to avoid hitting the anchor bolts, ensuring concrete fills every corner of the formwork. The top level of the short column must be strictly controlled, as it serves as the benchmark for steel column installation.
Step 6: Steel Column Installation and Final Fixation
Once the foundation concrete reaches the required design strength, the final "finishing touch" arrives.
Steel Column Hoisting: The prefabricated steel column is hoisted into place using a crane, aligning the bolt holes in the column base plate precisely with the pre-embedded anchor bolts.
Leveling and Fixing: The column's plumb and elevation are adjusted using nuts and leveling plates, checked with instruments like theodolites to ensure full compliance with the design position.
Welding Stiffener Plates: Often, pre-embedded base plates or direct welding are used between the steel column and the top of the concrete short column. To further enhance the connection's stiffness and strength, stiffener plates (or rib plates) are often welded around the column base, ensuring smoother and more reliable load transfer.
Grouting: Finally, the space between the steel column base plate and the concrete foundation top is filled with high-strength non-shrink grout, filling all voids to ensure uniform pressure transfer and truly integrating the steel column with the foundation.
Conclusion
The construction of an independent foundation for steel structures is an interlinked process requiring precision and excellence. From the initial excavation to the final erection of the steel column, each step embodies rigorous calculation, precise measurement, and standardized workmanship. It is this solid foundation, hidden from view, that silently bears the weight and ensures the safety of the entire steel structure building.
