I. Common Quality Accidents in Light Steel Structural Engineering
(1) Common quality accidents in space truss projects
1. Bending deformation or local fracture of members;
2. Failure of seam connection of rod seal or cone head;
3. Deformation or fracture of joints;
4. The weld seam is not full or has bubbles, slag inclusion and micro-cracks exceeding the prescribed standards.
5. The high-strength bolts are broken or pulled out from the spherical joints.
6. When the members collide at the joints and the upper chord is supported, the web member of the support and the supporting structure
To collide with each other;
7. Displacement of bearing nodes;
8. The deflection of the space truss is too large, which exceeds 1.15 times of the corresponding design value specified in the design.
(2) Common Quality Accidents in Portal Frame Engineering
1. Deformation and distortion of main components;
2. Embedded parts do not meet the requirements of drawings and specifications, the height difference exceeds the standard, and the spacing exceeds the standard.
3. Over-tolerance of overall verticality and overall plane bending of steel frames, end plate holes of beams and columns
Dislocation, size dislocation;
4. The weld seams of the main stressed joints are not full or have bubbles, slag inclusions and micro-cracks.
Exceeding the prescribed standard, etc.
5. The location of auxiliary stable structures such as support, tie rod and knee brace is unreasonable.
Or processing errors;
6. Secondary components do not meet the quality requirements.
II. Main Reasons
(1) Design reasons
1. The unreasonable selection of structural forms, unreasonable cross-section matching and neglect
The influence of initial bending and eccentricity of members, the calculation of low load and missing load in design
2. The material selection is unreasonable.
3. The choice of calculation method, hypothesis and computer program are not found.
4. After structural design calculation, material substitution is carried out without review, resulting in
The strength component of case super design value appears.
5. Wrong or incomplete drawings. If the dimension labeling is confused and the design instructions are not clear,
There are omissions in materials, process requirements, construction procedures and special requirements.
6. The construction of nodes is wrong and the details are not considered comprehensively.
(2) Processing reasons
1. Confused management, mixed use of different specifications, steel grades and materials;
2. The blanking size of the component is wrong, and the slenderness ratio of the component does not meet the design requirements.
3. No lining pipe or setting up of weld seam for grid member without cutting or butting
Requirements for welding;
4. Connection high strength bolts are not qualified;
5. Component processing is defective, and the angle deviation of bolt hole is large.
6. The weld quality is poor and the fillet size does not meet the design requirements.
(3) Reasons for installation of space truss
1. Uneven support points, unreasonable force and incorrect assembling in ground assembling
Differential accumulation, individual pole errors, resulting in force changes, resulting in grid or individual pole
2. The welding process and sequence are wrong, resulting in welding stress and deformation.
3. When hoisting as a whole, the selection of hoisting points is unreasonable, and the hoisting points are not reversed.
Force checking, bar overstress checking, deflection checking and the necessity of overstress checking
4. When hoisting as a whole, the lifting speed of each hoisting point is different, and the displacement and height difference are excessive.
Excessive allowable range leads to deformation and destruction.
5. Error in selection of construction scheme, not according to the form of grid structure and site
Reasonable selection of construction conditions, installation can not form a geometric invariant system.
Deformation and destruction;
6. The pre-embedded parts, pre-embedded bolts or the top of columns of space truss bearings deviate greatly and are in place.
Difficulties, forced positioning, resulting in changes in the bearing force conditions, rod deformation;
7. Installers are careless, the position of rods and ball angle are wrong.
8. When the upper chord is supported, the accumulation of errors is too large, which leads to the displacement of the support seat and the web rod.
Collision with support surface.
(4) Reasons for Installation of Portal Frames
1. When long components are transported and stacked, they are not laid uniformly and for a long time.
Causing distortion and distortion;
2. The position of the embedded bolt is not correct, and there is no re-measurement or correction during installation.
It results in the deformation and distortion of columns and beams, and the overall verticality and plane bending error of the steel frame.
3. The hole position of end plate of beam and column is not corresponding and dislocation, and the end plate is not aligned when installed.
When bolts are fastened, they are not fastened in sequence.
4. There are no operation or welder technical problems according to the welding rules in field welding.
Causes the weld not to be full or has the bubble, the slag inclusion, the micro crack;
5. Installation without detailed and careful understanding of the drawings, resulting in individual component locations
6. Before installation, no detailed construction plan was worked out according to the actual situation of the project.
Technical disclosure leads to process inversion and other phenomena.
7. Construction does not proceed in sequence and the steel frame does not form a stable structure.
The whole instability is caused by the construction of the working procedure.
8. When the steel column is rigidly connected to the inserting column foundation, the concrete can not reach the strength or the foot of the column.
Installation of upper components leads to structural instability.
(5) Use and other reasons
1. The service load exceeds the design load.
2. Use environment change;
3. Uneven settlement of foundation occurs.
4. Natural disasters.
3. Engineering examples
A factory with a span of 31.5 metres and a length of 78 metres has a sinusoidal quadrangular cone supported by the upper chord.
Bolted sphere space truss, the main structure of the roof space truss of the main factory building is suddenly completed during the construction period
The collapse of the body caused serious accidents.
Field investigation shows that many lower chord members are broken and bent, and some high strength snails are found.
Bolt breakage, web bar bending, bolt bending or fracture are common, and ball rod connection is broken.
The support of the space truss fell.
1. Processing Reasons: Material management is chaotic, and there is no need for access materials.
To test, the carbon content of individual rods is low, and the strength of individual high-strength bolts can not reach.
2. Construction Reasons: Construction is not constructed according to the design of construction organization.
The main cause of the overall collapse of the grid structure. When the space truss is installed, it is lifted as a whole first, and then it is lifted as a whole.
Bulk from one end to the other. When assembling to form a stable unit system, no
To observe and measure the displacement and deflection of the support seats of some space trusses, there is no network.
Adjustment and fixing of bracket support, without necessary support in the span of the grid, carry out high altitude
Bulk loading and roof construction lead to inadequate fastening of individual bolts and deflection of space truss
Large, the overall size changes, the force of the rod and bolted spherical joints does not conform to the design conditions.
The shear force of the joint bolts is too large and the bolts break, which leads to the collapse of the grid.
When the web rod at the support is connected with the bolt ball, individual bolt holes do not correspond to each other.
Simple welding, its bearing capacity is only about 40% of the design value.
Construction was not carried out in accordance with the procedures and specifications. Due to the tight construction period, the construction was carried out in the main frame.
The roof construction team began to enter without the body being completed and the support being welded.
During roof operation, the roof load increases, which accelerates the overall collapse of space truss.