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Q1: How many types of connections are there for steel structures? B: The main methods of connecting steel structures are welding, bolting, and riveting. Q2: What are the main classification methods for bolts? B: Classified by performance level into 3.6 grade, 4.8 grade, 5.6 grade, 6.8 grade, 8.8 grade, 9.8 grade, 10.9 grade... and so on. Bolts of grade 8.8 and above are made of low-carbon alloy steel or medium-carbon steel, and are heat-treated, primarily through quenching and tempering. They are generally referred to as high-strength bolts, while bolts of grade 8.8 and below are usually called ordinary bolts. The digits before and after the decimal point represent the ratio of the theoretical tensile strength to the yield strength of the bolt material, respectively. https://upload-images.jianshu.io/upload_images/23123608-60fde69b32af0853.jpeg?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240 Common ordinary bolts include hex bolts, double-headed bolts, foot bolts, etc.; high-strength bolts are divided into torsion-shear type and large hexagonal type. Based on the mode of force transmission, they are classified into shear-resistant bolts, tensile-resistant bolts, and bolts subjected to both shear and tensile forces. Shear connection: External forces perpendicular to the axis of the member are transmitted through the pressure of the screws and shear forces; there is a tendency for alternating movement between the plates ； Tensile connection: External forces parallel to the axis of the rod are transmitted through the tension in the screws; there is a tendency for the plates to separate from each other ； Tension-shear combined action: Relying on the screw, it transmits not only external forces perpendicular to the axis of the rod but also those parallel to the axis of the rod. There is a tendency for relative interlacing and separation between the plates. https://upload-images.jianshu.io/upload_images/23123608-9cc888ff695f39fb.jpeg?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240 Based on calculation and design methods, high-strength bolts can be classified into friction connections and compression connections. Frictional connection: The shear force is transmitted solely by the frictional resistance generated by the compressive pressure; the design criterion is that the shear force should not exceed the frictional resistance (sliding of the contact surfaces is not allowed). Load-bearing connection: Allows sliding of the contact surfaces, with the ultimate load capacity in the event of connection failure serving as the design criterion. The bearing capacity of the joint is higher than that of the friction-type joint, and the joint is compact, but its shear deformation is greater than that of the friction-type joint. Q3: What are the requirements for bolt arrangement and bolt spacing? B: Bolt arrangements can be divided into parallel and staggered arrangements. Parallel bolt arrangements are simple, neat, and compact; the connecting plates required are small in size, but the cross-section of the components is reduced significantly ； The staggered bolt arrangement is not compact; the connecting plates used are large in size, resulting in lower stress on the cross-sections of the components. The distance between the edges of the bolts as well as the distance in the middle should not be too large, to prevent poor adhesion between the steel plates and corrosion of the steel due to moisture ； In the case of tensile members, as well as when the intermediate distance and edge distance are too small, it is not advisable to significantly reduce the cross-section of the connecting plate; this could lead to damage to the net cross-section along straight or curved lines, resulting in shear failure of the connected steel elements ； In compressed members, when the spacing between bolts along the load direction is too large, the connection plates tend to protrude. The maximum and minimum allowable distances for bolts are shown in the table below. https://upload-images.jianshu.io/upload_images/23123608-3ceaf3d984d3c113.jpeg?imageMogr2/auto-orient/strip%7C.imageView2/2/w/1240 What is the working performance of bolt shear connections in Q4? A: Shear connection is the most common type of bolted connection. Through shear tests, a curve showing the relative displacement relationship of forces between points a and B was obtained. There are four stages from loading to structural damage. ① Elastic stage of frictional force transmission (O1 straight-line segment): The load is transmitted through the friction at the indirect contact surface between the plates, while the gap between the anchor rod and the hole wall remains unchanged. In the elastic phase, which is very short, it can be omitted. ② Relative sliding stage (12 horizontal lines): As the load increases, the shear force reaches its maximum friction value, causing relative sliding between the plates until the bolt shaft comes into contact with the wall of the hole. ③ Elastoplastic stage (curve 23): In addition to shear force, the bolt shaft is also subjected to bending moment and axial tensile force, and the hole walls experience compression. When the value reaches “3”, the bolt or connecting plate reaches its elastic limit. ④ Failure stage (curve 34): During this stage, even a small increase in load rapidly increases the shear deformation of the joint, until the joint eventually fails. The load corresponding to the highest point “4” on the curve is the ultimate load. https://upload-images.jianshu.io/upload_images/23123608-a9f411b4e09a55eb.jpeg?imageMogr2/auto-orient/strip%7C.imageView2/2/w/1240