Steel truss floor slab is a commonly used floor system in steel structure prefabricated buildings, which has advantages such as factory prefabrication, strong integrity, and fast construction speed. Reasonable design can effectively optimize floor load, reduce steel beam section, and lower overall steel consumption. However, in actual engineering design, a large number of details and misunderstandings frequently occur. Seemingly routine design omissions can completely change the transmission path of floor forces, significantly increase the stress burden on steel beams, force steel beams to increase their cross-section and wall thickness, and ultimately cause a surge in overall steel consumption, completely offsetting the energy-saving and cost reducing advantages of floor slabs. This article outlines seven common misconceptions in high-frequency design, clarifies the hazards and optimization strategies, and provides reference for engineering design.
Firstly, blindly enlarging the selection of floor slabs and excessively redundant reinforcement. Some designers, in order to avoid risks and without considering the actual span and load, arbitrarily choose high configuration plate types, increase the height of trusses, thicken steel bars, and densify web members. This directly increases the floor dead load, and the steel beams need to improve their bearing capacity to adapt to the load, so the section size can only be increased, resulting in a waste of steel usage. The design should be selected based on actual working conditions and standards, and redundant designs without basis should be eliminated.
Secondly, the span of the floor slab does not match the spacing between the steel beams. Many projects have arbitrary arrangement of steel beams, which are misaligned with the standard span of the floor slab, resulting in mismatched sizes and spans. Overspan laying can lead to excessive deflection and uneven stress distribution on the slab surface, resulting in local stress concentration and additional increase in steel beam load, forcing steel beams to be reinforced and weighted. The design should follow the principle of first determining the beam spacing and then selecting the plate type to ensure precise compatibility between the two.
Thirdly, ignore the superposition of temporary construction loads. Most designs only account for the load during the usage phase, ignoring the construction pile load and vibration load during concrete pouring. Excessive temporary loads will increase the instantaneous stress on the floor. In order to reserve safety margins, designers will passively enlarge the specifications of steel beams, indirectly increasing their own weight.
Fourthly, the design of the overlap length at the board end is insufficient. Insufficient overlap size can lead to poor load transmission, poor support stability, and potential deformation hazards on the floor. To control structural deformation and ensure safety, it is necessary to increase the cross-section of steel beams to compensate for support defects, resulting in unnecessary weight gain.
Fifth, randomly opening floor holes without optimization. A large number of openings in the mechanical and electrical pipelines without proper reinforcement will weaken the overall integrity of the floor slab, damage the force transmission system, and cause local stress concentration on the steel beams, forcing them to upgrade and reinforce.
Sixth, ignore concrete shrinkage and temperature stress. The design does not reserve expansion allowance, which can easily cause floor cracking and abnormal stress. In order to avoid structural risks, the safety factor of steel beam design is forced to be enlarged, increasing the cost of steel.
Seventh, the force distribution design of the primary and secondary beams is unreasonable. The load transmission path is chaotic and the force distribution is uneven. Some steel beams are overloaded and can only meet the bearing capacity requirements by increasing the cross-section. In summary, precise and standardized detail design is the key to leveraging the advantages of truss floor slabs and strictly controlling the self weight of steel beams.
