Structural Selection
Beam and column setting
(1) Commonly used Ⅰ cross-section beam economic span of 6 ~ 12m, the design must consider the upper structure of the building to choose.
(2) Secondary beams are conducive to the uniform distribution of loads and clear transmission paths, the spacing is generally taken as 1.5 ~ 2.5m, in the vibration equipment concentration or load should be appropriately reduced.
(3) Steel secondary beam is generally articulated with the main beam, can reduce the beam of the span moment and deflection, but must consider the impact of welding workload.
(4) Considering the economic rationality factor can choose box-shaped steel frame column section, no strong and weak axis of the structure is more reasonable, but the amount of assembly welding process is difficult.
(5) frame columns can choose to connect the less difficult rolled wide flange H-beam, but must be considered when the floor height is high enough to meet the requirements of the weak axis of the slenderness ratio, if not to meet the choice of cross-section steel columns.
Floor setting
(1) the choice of combined floor, in the use of the stage by the compression steel plate equivalent to the concrete floor tensile reinforcement, must control the amount of galvanised steel and plate thickness, consider the fire safety factors brought about by the requirements of the economic indicators.
(2) Selection of non-composite floor can be calculated according to the ordinary reinforced concrete floor slabs, compression steel plate will bear more loads, construction should be done before the rust treatment; this way to save money on fire protection.
(3) When the floor is set up in the steel beams must be set at the top of the cylindrical head bolts through the steel plate, and according to the floor span to determine the diameter of the bolts and column spacing at the top of the column, and high pressure-type steel plate must be not less than 3cm on the top surface, higher than the top surface of the concrete layer of protection of not less than 1.5cm.
Node optimisation
Beam column node
(1) beam-column nodes are usually connected rigidly to ensure that the upper and lower flanges of the beam are firmly welded to the column flange, and the web is connected to the shear plate of the column flange. For buildings with seismic requirements, horizontal stiffening ribs of equal thickness should be set up with the beam flanges and welded to the column with full penetration.
(2) In each beam flange corresponding position to set the horizontal stiffening rib of the column can strengthen the stiffness and stability of the beam-column node, for the cross-section height of the beam web can increase the height of the local height, but must pay attention to the axil flange slope.
Assembling node
(1) For the higher height of the column and the larger span of the beam, often choose to use multi-segment field splicing measures to lengthen, must pay attention to the column joints are not in the frame node plastic zone, and must meet the ultimate load bearing capacity requirements.
(2) Ⅰ zigzag section column joint flange can be used full penetration bevel welding, the web using high-strength bolt connection.
(3) The cantilever beam section outside the column is connected with the intermediate beam section by full penetration welding at the wing edge and high-strength bolt connection at the web; the wing edge and web are welded by full penetration welding.
Through the above optimisation design, the stability and rationality of the steel structure can be increased, and at the same time, the testing and identification of the steel structure should not be neglected, and the bearing capacity should be strictly controlled and the reinforcement measures should be selected according to the actual situation.
Detection and appraisal
(1) Steel structure testing includes appearance quality testing; component size and flatness testing; weld and bolt connection testing; steel corrosion testing; coating thickness testing.
(2) When determining the yield strength of steel, the yield point stress should be taken for the steel with obvious flow amplitude; the condition yield strength should be taken for the steel without obvious flow amplitude.
(3) Detect the chemical composition of steel, control the carbon content to ensure the balance of strength, plasticity, weldability and rust resistance; control the manganese content to ensure the balance of strength and brittleness; control the silicon content to control the balance of strength and plasticity, weldability and rust resistance; control the phosphorus content to ensure the balance of strength and rust resistance and so on.
(4) Measure the coating thickness, including the thickness of fireproof coating and anti-corrosion coating thickness, multiple measurements to determine the location of the thin layer to make up for the coating.
(5) Measure the deflection of steel mesh frame, and measure the central part of the lower chord if the span is not more than 24m; measure the central part of the lower chord and four equal points of the lower chord span if the span is more than 24m.
Reinforcement
Column reinforcement
(1) Use steel plate or steel section reinforcement to strengthen the original column structure through welding or high-strength bolts; additional support can also be provided to reduce the free length of the column to improve the load-bearing capacity; attention must be paid to the existence of serious defects and damage to the steel structure must be calculated structural strength, stiffness and stability and then reinforced.
(2) reinforced concrete reinforcement around the steel column, pay attention to clean up the surface to increase the bonding effect, and ensure that the external structure and the original steel column to form a whole, so as not to play a reinforcing effect, but to increase the load.
Column foot reinforcement
(1) Increase the column foot stiffening ribs, reduce the calculated bending moment of the base plate, can be poured between the foot of the column steel casting concrete, so that the foot of the column base plate to become a rigid block; pay attention to clean up the surface to increase the bonding effect before construction.
(2) Additional anchor bolts can be added to the foot of the column. When the foundation is wide, holes can be drilled, additional anchor bolts can be inserted, epoxy mortar or sulphur mortar can be poured, the whole foot of the column can be wrapped up and the new reinforcement bars can be inserted into the foundation and welded with the original reinforcement bars.
Steel structure buildings are widely used in the field of ultra-high-rise, due to the advantages of high stiffness and light self-weight, etc. are widely accepted for use. Increasing the design stability of steel structure, detecting and identifying potential safety hazards, and reinforcing the reinforcement in combination with the actual situation are the technical points that need to be accurately mastered in the project.
