300 Core Technical Issues in Reinforcement Steel Engineering (III)

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300 Core Technical Issues in Reinforcement Steel Engineering (III) 201. In the flat method, what component does GYZ represent? Answer: Construct edge wing wall columns. 202. In the flat method, what do b and b1, b2 represent? Answer: The width of the column cross-section and its width on either side of the axis. 203. In the flat method, what do h and h1, h2 represent? Answer: The height of the column cross-section and the heights on both the upper and lower sides of the axis. 204. In the Pingfa method, what does Ln represent? Answer: The larger of the net spans on either side of the support. 205. In the flat method, what structural requirement does Ln/4 represent? Answer: The length of the two rows of bars at the support that extend into the net span. 206. In the flat method, what code is used to represent roof beams? Answer: WL and WKL. 207. In the flat method, what is used to represent grid beams? Answer: JSL. 208. What are the characteristics of the reinforcement configuration for non-frame beams? Answer: The stirrups are not densely arranged, and the anchorage length of the lower longitudinal bars extending into the support is 12d. 209. What do 235, 335, and 400 in the specifications for steel bars mean? Answer: Newton (force). 210. Where are 8d right-angle hook bends used? Answer: The length of the hook formed when the rebar at the top of the frame column is bent inward toward the column before bending downward. 211. Where are 12d right-angle hooks used? Answer: Length of the hook below the column reinforcement and length of the hook above the top reinforcement of the column ； The direct anchorage length of the longitudinal bars under non-frame beams, as well as the hook length of the longitudinal bars in foundation raft beams. 212. For the rebar mesh at the bottom of an independent foundation, which direction’s rebar is on the lower layer? Are the rebar in that direction on the upper layer? Answer: For independent foundations, the long-reinforcement bars are placed at the bottom, while the short-reinforcement bars are placed at the top. 213. How is the distance from the starter tendon to the edge of the foundation determined? Answer: It is a comparison between 75mm and S/2 (half pitch), which means half the pitch. 214. What is a composite stirrup? What is a non-composite stirrup? Answer: A composite stirrup is a group formed by combining two or more stirrups together ； One stirrup is not considered a proper stirrup. 215. Should the stirrups at the base of the column foundation be composite stirrups or non-composite stirrups? Answer: At the base of a column foundation, since it only serves to fix the longitudinal reinforcement, it generally does not need to meet the requirements for stirrups. 216. The longitudinal reinforcement bars of columns cannot overlap in one cross-section; what is the offset length required in the case of welded connections? What is the offset length in the case of bonded connections? Answer: In the case of welding, the larger of 35d and 500 is taken as the offset length. Under binding conditions, it is 0.3Lae (0.3 times the lap length) 217. What is the distance between the longitudinal reinforcement of columns and the non-connected area in the adjacent layer of the foundation? What is the unconnected area on the first floor? Is there a difference between welding and binding connections? Answer: The non-connected area from the base adjacent layer is 1/3 of the clear height; the first floor also has a clear height of 1/3. There is no difference between welding and binding. 218. Why is the length of the stirrup hook 11.9d? Answer: 10d + 1.9d. 10d is the length of the straight section of the stirrup hook; for seismic structures this value is 10d (while for non-seismic structures it is 5d). 1.9d represents the extension length of the hook at a 135-degree angle. 219. How is the spacing of stirrups in the lap area determined when the longitudinal bars of columns are tied together? Answer: The encrypted area is 100, 5d; the smallest value among these three values is taken as the spacing for the reinforced bars in the encrypted zone. 220. In the concentrated notation for beams, what does the (3) in KL5(3)300*500 mean? What does (4) in ￠10@100/200（4） mean? 2Φ25+（2￠14） ； In 2Φ25, what does the previous 2Φ25 mean? What does the latter 2Φ25 mean? What does (2￠14) in the middle mean? Answer: KL5(3) 300*500 – the (3) indicates three spans; in ￠10@100/200, the (4) denotes four leg stirrups; 2Φ25+(2￠14) ； In 2Φ25, the first 2Φ25 indicates that there are two grade 25 rebars as the vertical reinforcement in the upper part of the beam; the second 2Φ25 indicates that there are two grade 25 rebars as the vertical reinforcement in the lower part of the beam. The middle part, (2￠14), means that no negative reinforcement is used in the mid-span, and instead two grade 14 rebars are used as the stirrups. 221. What does 5Φ25 2(-2)/3 mean in in-situ marking? Answer: It indicates that there are 5 grade-2, 25-mm rebar bars in the lower part of the beam, arranged in two rows – 2 bars in the upper row and 3 bars in the lower row; the 2 bars in the upper row do not extend into the supports. 222. Under what circumstances are the longitudinal reinforcement bars in beams anchored directly at the beam ends? Under what circumstances is a bent anchor used? Answer: When the bearing width minus the cover thickness ≥ the anchorage length LaE (La), a direct anchorage design is used ； When: 0.4LaE(La) ≤ support width – cover layer < anchorage length LaE(La), a bent-anchorage design is used. 223. At what height must stirrups be added to a beam? Answer: When the web height is ≥ 450 mm. 224. Where does the upper lap of the longitudinal reinforcement of a beam occur? Answer: The lap position of the top longitudinal reinforcement should be within 1/3 of the clear span ； 225. At the junction of a beam and a column, which rebar should pass through: that of the column or that of the beam? Answer: At the junction of a beam and a column, since the column serves as the support for the beam, the column is primary while the beam is secondary; the stirrups of the column run through, while those of the beam extend to the side of the column. 226. Under what conditions are stirrups used in beams? What is the main function of the stirrups? Answer: Stirrups are installed when the number of longitudinal bars is less than the number of limbs in the composite stirrups; these stirrups serve primarily to secure the intermediate stirrups in place. 227. What is the difference in anchorage length between the longitudinal bars on the structural side of a beam and those on the torsion-resistant side? Answer: The torsion-resistant lateral longitudinal bars, similar to the lower reinforcement in beams, also have two forms of anchorage at the end supports – bent anchorage and straight anchorage; straight anchorage is used at the intermediate supports ； The length of the longitudinal reinforcement on the construction side extending into the support is 15d. 228. What is the difference between the first-level seismic resistance requirements for frame beams and the reinforced zones for second to fourth-level seismic resistance? Answer: For first-degree seismic resistance, the range of the reinforced zone in frame beams is ≥2hb, and ≥500 ； For seismic resistance levels 2 to 4, the range of the reinforced zone in frame beams is ≥1.5hb and ≥500. 229. Should the hanging bars be placed on the main beam or the secondary beam? Answer: The suspension bars should be placed on the main beam; when the beam height hb ≤ 800, the slope of the suspension bars is 45° ； 230. What is the difference between non-frame beams and floor frame beams? Answer: 1. The anchorage lengths are different; for frame beams, the anchorage length is LaE, while for non-frame beams it is La. 2. The length of the negative reinforcement at the end supports that extends into the beam: for frame beams, it is 1/3 of the clear span; for non-frame beams, it is 1/5 of the clear span. 3. Length of the lower rebar extending into the support: for frame beams, it depends on whether a straight or bent anchor is used; for non-frame beams, it is 12d. 231. What is the length to which the negative reinforcement of the stairs extends into the stair slab? Answer: Ln/4 (here, Ln is the horizontal net length of the tread; it should be calculated as the slant length). 232. How to calculate the slope coefficient of a staircase? Answer: It is a coefficient obtained by using the formula based on the height of the step, plus the formula based on the width of the tread plate, taking the square root of that value, and then dividing by the width of the step. 233. If the bottom rebar of a staircase is anchored directly into the floor slab, how should the net span length of the staircase be calculated in such a case? Answer: If the bottom reinforcement is anchored directly in the floor slab, the first step serves as the anchorage point; therefore, the length of one step must be deducted when calculating the net length. 234. How many common situations arise when the longitudinal reinforcement of structural columns is connected to frame beams? What are they respectively? Answer: There are three ways to connect ； They are respectively embedded iron parts (parts reserved during the casting of cast-in-place frame beams), reserved reinforcement bars (reinforcement bars reserved during the casting of cast-in-place frame beams), and inserted reinforcement bars (reinforcement bars inserted after drilling holes in the frame beams). 235. At the intersection of a structural column and a ring beam, which rebar should pass through – that of the structural column or that of the ring beam? Answer: In this case, the structural columns are primary, while the ring beams are secondary. The stirrups of the structural columns pass through, and the stirrups of the ring beams reach the outer side of the structural columns. 236. What is the length of the lintel that extends into the support? Answer: Generally, 250 at one end ； 237. Why is the cover thickness for the longitudinal reinforcement in frame beams specified as 25 millimeters instead of 30 millimeters? Answer: Since frame columns bear compression forces while frame beams bear tension forces, too thin a cover layer reduces the effective height of the beams and diminishes the load-bearing capacity of their longitudinal reinforcement. 238. What is the minimum specified bending radius for stirrups? What is the specified angle for the bend hooks of stirrups? Answer: Not less than 2d ； The hook angle is 135 degrees. 239. What is the specified length of the hook for stirrups? Answer: 5d for non-seismic design ； The greater of 10 days and 75 millimeters for seismic or torsional resistance. 240. In which direction are the hooks of beam stirrups usually oriented? In what circumstances should the hooks of beam stirrups point downward? Answer: Upward, mainly toward the side that is not under tension, toward the side containing the concrete slab. Upward-reverse beam, with the slab located below the beam. 241. Are the hooks of the stirrups in beams and columns all on the top? Answer: No, the 4 corners should be offset from each other. 242. What is the function of stirrups in beams? Answer: It serves to fix and restrain the longitudinal bars, as well as to bear a portion of the shear force. 243. Where are the top stirrups of a beam indicated using the flat method? What is another name for the upper corner reinforcement in a beam? Answer: At the centralized annotation location. Top continuous bar or full-length bar of the beam. 244. Where is it required to connect the continuous top bars of a beam? What were the rebars at the supports of beams called before? Answer: At the midpoint of one-third of the span of the beam. Bending reinforcement or negative moment reinforcement. 245. How long is a row of reinforcement at the end supports of a beam required to extend into the net span? Answer: One-third of the net span. 246. How long are the two rows of rebars at the end supports of a beam required to extend into the clear span? Answer: One-quarter of the net span. 247. How is the length of a row of reinforcement bars at the intermediate support of a beam calculated? Answer: Take one-third of the larger net span on each side multiplied by 2, and add the width of the middle support. 248. How is the length of the two rows of bars at the middle support of the beam calculated? Answer: Take one-quarter of the larger net span on each side multiplied by 2, and add the width of the middle support. 249. What does Lae mean? What is it usually called? Answer: The seismic anchorage length is commonly referred to as the straight anchorage length. 250. What does Lle mean? How many ties should be used within the overlap area? Answer: The lap length should be secured with no fewer than 3 ties. 251. What does the 50% steel bar lap area percentage mean? Answer: Half is overlapped and half is not overlapped. 252. For a 25% area percentage, how many of the 8 rebar bars are allowed to be connected in the same section? Answer: 2. 255. Where is it permitted to splice the longitudinal reinforcement at the bottom of a beam? Answer: At one-quarter of the way down from the beam, near the support. 256. Under what circumstances is 0.4Lae used? Answer: When direct anchoring is insufficient. 257. What are the various construction methods for the top edge nodes of a beam? Answer: 1. 65% of the longitudinal reinforcement at the column edge shall be anchored into the beam by 1.5Lae ； 2. The reinforcement on the beam is anchored into the column by 1.7Lae. 258. When the heights of the left and right spans of a beam are different, under what circumstances can the longitudinal reinforcement of the beam be bent to pass through? Answer: Bending is possible when the ratio of the support width to the difference in beam height is less than one-sixth. 259. When the cross-section of a beam changes and the longitudinal reinforcement cannot be bent to pass through, how should this be handled? Answer: A curved anchor on one side, and a straight anchor on the other. 260. What should be done when the cross-section of a column changes and the longitudinal reinforcement cannot be bent to pass through? Answer: The rebar in the lower column is bent and anchored 200 mm into the edge of the upper column, while the rebar in the upper column is anchored straight into the beam for a length of 1.5 times Lae. 261. For seismic-resistant frame columns on standard floors, what are the three specified values for the non-connection zone? Answer: 1. Greater than 1/6 of the column net height ； 2. Greater than 500mm ； 3. Greater than the long side dimension of the column cross-section. 262. In the non-connection zone of seismic frame columns, there is a portion equal to three-halves of hn – where does this refer to? Answer: Including the basement, it is the first floor from the bottom. 263. How many types of connections are there for steel bars? Answer: Overlap ； Welding ； Mechanical connection. 264. Under the new circumstances of the current era, what is the best connection method for rebar? Answer: Threaded connections are the best. 265. What does non-contact connection of steel bars mean? Why is non-contact connection of steel bars being promoted nowadays? Answer: A specified distance is left between the two overlapping rebar bars. Ensure the bond between concrete and steel reinforcement. 266. In the flat method, what are the various ways to indicate the total score? Which takes precedence, centralized annotation or in-situ annotation? Answer: 2 types, centralized annotation and in-situ annotation. In-situ annotation values take precedence. 267. Why does the content of the concentrated annotation appear again at the in-situ annotation location? Answer: Local structural changes occur, such as changes in cross-sectional height or width, changes in elevation, or changes in reinforcement; design errors may also be present. 268. Should the horizontal distribution bars in shear walls be placed inside or outside the longitudinal bars of the wall columns? Answer: Leave it outside (if the design does not require otherwise). 269. In shear walls, for the diagonal cross-reinforcing bars, where is the zone with increased stirrup density? Answer: At the intersection of the hidden braces along the line connecting the upper and lower openings. 270. When does a opening in a shear wall need to be flanked by hidden beams and columns? Answer: 800mm. 271. At what size of openings in shear walls are reinforcement bars required at the edges of the openings? Answer: When it is greater than 300 mm and less than 800 mm. 272. What are the main types of slab staircases? Answer: Straight type, bottom-folding type, top-folding type, mid-flat type, rotating type. 273. How should the inclined length of the tie bars in a straight-flight staircase be determined? Answer: One quarter of the net span of the inclined tread length plus the length extending into the beam multiplied by the k value. 274. In slab-type staircases, what is the inherent relationship between the lower main reinforcement and the upper stirrups? Answer: Design it at half the strength of the lower longitudinal reinforcement. 275. In slab staircases, what does the thickness of the stair slab refer to, and what symbol is used to represent it? Answer: The vertical distance from the corner of the step to the bottom of the slab. Denoted by h. 276. Where is spacing @100 most commonly used? Where is spacing @50 most commonly used? Answer: At the reinforcement stirrup densification area. Additional stirrups at the junction of primary and secondary beams. 277. Where is spacing @150 most commonly used? Where is spacing @200 most commonly used? Answer: Wall reinforcement bars, slab reinforcement bars, and wall/column stirrups. Ordinary stirrups, distributed reinforcement in walls and slabs. 278. How many categories are there for lumbar muscles? How should the lumbar tendons be arranged in the beam? Answer: There are two types: structural lumbar muscles and torsion-resistant lumbar muscles. They are arranged at equal intervals within the range of the beam clear height minus the cover thickness. 279. What is the difference between anti-torsion lumbar muscles and structural lumbar muscles? Answer: Different codes are used for different functions; those for anti-torsion lumbar muscles start with N, while those for structural lumbar muscles start with G. The anchorage of anti-torsion waist reinforcement is the same as that of longitudinal beam reinforcement; the anchorage length for structural waist reinforcement is 15d. 280. To which category does the lumbar tendon that requires 15 days of anchoring belong? What is the specified maximum vertical spacing for the lumbar muscles? Answer: It belongs to the structural lumbar muscles. Not more than 200 mm. 281. For diaphragm beams and hidden beams with straight anchors at both ends, how is the beam length determined? Answer: The length of the beam is determined by the net span plus twice the anchorage length. 282. What are the differences in the reinforcement design between floor beams and roof beams? Answer: The rebar in floor beams can be anchored directly, while the rebar in roof beams cannot be anchored directly; in addition, an increased anchorage length is required. 283. What is a simply supported beam, what is a tie beam, and what is a cantilever beam? Answer: A beam with only two supports is called a simply supported beam ； A beam with three or more supports that are connected to each other is called a connecting beam ； A beam that has only one support and is suspended at one end is called a cantilever beam. 284. How are the cross-sectional heights at the root and tip of a cantilever beam represented in the flat method? Answer: It is represented using a slash /. 285. What is the anchorage length of the lower reinforcement in a cantilever beam at its root? Answer: 12 times the diameter of the rebar; for smooth rebar, 15 times the diameter. 286. What is the length of the upper two rows of rebar in the cantilever beam within the cantilevered area? Answer: 0.75 times the net length of the cantilevered section. 287. Under what conditions must the upper middle rebar of a cantilever beam be bent downward? Answer: When the ratio of the net length of the cantilevered section to the height at the root of the cantilever beam is greater than one-quarter. 288. In the flat method, what does Ln represent? Answer: The larger of the net spans on either side of the support. 289. In the flat method, what structural requirement does Ln/4 represent? Answer: The length of the two rows of bars at the support that extend into the net span. 290. What are the characteristics of the reinforcement configuration for non-frame beams? Answer: The stirrups are not densely arranged, and the anchorage length of the lower longitudinal bars extending into the support is 12d. 291. Under what circumstances is the 10d value of steel bars used? Answer: The length of the right-angle hook for non-seismic, non-frame longitudinal reinforcement, the length of the hook for reinforcement in cap beams and slabs, and the length of the straight section after bending for 135-degree inclined hooks in stirrups. 292, 0.75L, under what circumstances does it occur? What is the special significance of LaE? Answer: When there are two rows of bars at the upper part of the cantilever beam. Used when seismic resistance requirements apply. 293, 0.4LaE, 0.7LaE – what kind of specialized values are these exactly? Answer: Minimum limit value for bent anchors. The latter is the minimum limit for mechanical anchorage. 294. Under what circumstances is 0.8LaE used? Answer: The length of the bent section at the overlap of the horizontal wall reinforcement in corner columns. 295, 1.5LaE, 1.7LaE – what are they used for? Answer: For top-layer edge nodes, it is the anchorage length of the vertical column reinforcement extending into the beam upon termination. Bending length of the upper reinforcement bars in the beam. 296. Where are 0.3LIE and 1.3LIE used? Answer: The clear distance between adjacent lap joints of the column longitudinal reinforcement. The distance between the center points of adjacent lap joints of the column longitudinal bars. 297. What area does hn/3 refer to? What area does hn/6 refer to? Answer: The non-connection zone of the rebar at the bottom of the base seismic frame columns and the reinforced zone of the stirrups. The non-connection zones and the reinforced zones of stirrups at the top and bottom of the seismic frame columns in all layers except the base layer. 298. What do hc and hb mean in the flat method? What does 0.5hc+5d refer to under what circumstances? Answer: It indicates the length dimension of the column cross-section and the height dimension of the beam. The direct anchorage length of the longitudinal bars at the bottom of the beam at the middle support. 299. What is the definition of a small wall limb shear wall? Answer: A short wall limb refers to a shear wall whose length is no more than 3 times the wall thickness. In what situations are 300, 1.5hb, and 2hb used in the stirrup reinforcement zones? Answer: Seismic resistance levels 2 to 4 and level 1!