【正文】 under these premises, the two joined to form the National Basketball Association (NBA) in 1949. A rival American Basketball Association (ABA) was inaugurated in 1967 and challenged the NBA for college talent and market share for almost ten years. In 1976, this league disbanded, but four of its teams remained as NBA teams. Unification came just in 。s game by recognizing it as an Olympic event in 1976. Again, television coverage of the Olympics has been exceptionally important in drawing attention to international teams. The first professional men39。s game changed radically in 1971 when separate rules for women were modified to more closely resemble the men39。 its construction and size of 30 in (76 cm) were ruled official in 1949. The rulesetters came from several groups early in the 1900s. Colleges and universities established their rules mittees in 1905, the YMCA and the Amateur Athletic Union (AAU) created a set of rules jointly, state militia groups abided by a shared set of rules, and there were two professional sets of rules. A Joint Rules Committee for colleges, the AAU, and the YMCA was created in 1915, and, under the name the National Basketball Committee (NBC) made rules for amateur play until 1979. In that year, the National Federation of State High School Associations began governing the sport at the high school level, and the NCAA Rules Committee assumed rulemaking responsibilities for junior colleges, colleges, and the Armed Forces, with a similar mittee holding jurisdiction over women39。 Australia, China, and India between 1895 and 1900。s original players were Canadians, and the game spread to Canada immediately. It was played in France by 1893。 the ball was the objective. To score, the ball had to be shot through a horizontal, elevated goal. The team with the most points at the end of an allotted time period wins. Early in the history of basketball, the local YMCAs provided the gymnasiums, and membership in the anization grew rapidly. The size of the local gym dictated the number of players。s Christian Association (YMCA), which later became Springfield College. Naismith (18611939) was a physical education teacher who was seeking a team sport with limited physical contact but a lot of running, jumping, shooting, and the handeye coordination required in handling a ball. The peach baskets he hung as goals gave the sport the name of basketball. His students were excited about the game, and Christmas vacation gave them the chance to tell their friends and people at their local YMCAs about the game. The association leaders wrote to Naismith asking for copies of the rules, and they were published in the Triangle, the school newspaper, on January 15,1892. Naismith39。s ball is in (7274 cm) in circumference. The covering of the ball is leather, rubber, position, or synthetic, although leather covers only are dictated by rules for college play, unless the teams agree otherwise. Orange is the regulation color. At all levels of play, the home team provides the ball. Inflation of the ball is based on the height of the ball39。s National Basketball Association (WNBA) playoffs. And it has also made American heroes out of its player and coach legends like Michael Jordan, Larry Bird, Earvin Magic Johnson, Sheryl Swoopes, and other great players. At the heart of the game is the playing space and the equipment. The space is a rectangular, indoor court. The principal pieces of equipment are the two elevated baskets, one at each end (in the long direction) of the court, and the basketball itself. The ball is spherical in shape and is inflated. Basketballs range in size from in (7276 cm) in circumference, and in weight from 1822 oz (510624 g). For players below the high school level, a smaller ball is used, but the ball in men39。 （ 4）驗(yàn)算配筋率 實(shí)際配筋率 % 30 ???? bhA s? % ?? 。 ② 若由于施工質(zhì)量原因，實(shí)測(cè)混凝土強(qiáng)度僅 達(dá)到 C20，試問(wèn)按 ① 問(wèn)所得鋼筋面積的梁是否安全？ MPafcd ? ， MPafsd 280? ， ?b? ， 0 ? ? 假設(shè) 40sa? mm，則有效高度 mmhh 51040550400 ????? 。m。 2234000 780300syNA m mf? ? ? 選用 4 16（ 2804sA mm? ）能夠滿(mǎn)足要求。求截面配筋。 解： 2/300 mmNf y ?? 2/ mmNfc ? （ 1）確定穩(wěn)定系數(shù) ? mmHl 56000 ?? ， 144 0 0/5 6 0 0/0 ??bl ，查附表 33，得 ?? （ 2）計(jì)算縱向鋼筋截面面積 21692300)(1 mmAfNfA cys ?????????????? ???? ? （ 3）驗(yàn)算配筋率 %,% 1692 ??????? AA s? 而 %3? ，滿(mǎn)足。梁中已配有雙肢 8? 箍筋，試求 ： 梁在正常使用期間按斜截面承載力要求所能承擔(dān)的荷載設(shè)計(jì)值 q 。 （ 4）求箍筋數(shù)量并驗(yàn)算最小配筋率 10)( 30??? ????? hf VVsAyvcsv 選雙肢箍Ф 8（ mmAsv ? ， 2?n ）代入上式可得： mmSmmnAAs svsv m a x1 ?????? ? 取 mms 100? ，可得： % % m i n, ????? ??? yvtsvsvsv ffbsA ?? ? 滿(mǎn)足要求 q 作用下的矩形截面簡(jiǎn)支梁，安全等級(jí)二級(jí)，處于一類(lèi)環(huán)境，截面尺寸 20 0 m m 55 0 m mbh? ? ?，混凝土為 C30級(jí)，箍筋采用 HPB235級(jí)鋼筋。 解：（ 1）確定計(jì)算參數(shù) 2/300 mmNf y ? ， 2/210 mmNf yv ? ， 2/ mmNfc ? ， 2/ mmNft ? ， ?c? ，mmahhh sow 51535550 ?????? （ 2）驗(yàn)算截面尺寸 ???bh w ，屬一般梁 kNVkNNbhf occ 2503833 8 3 0 3 m a x ???????? ?? 截面符合要 求。 ，處于一類(lèi)環(huán)境，安全等級(jí)二級(jí)，混凝土強(qiáng)度等級(jí)為 C25，梁的截面尺寸為25 0 m m 55 0 m mbh? ? ?， 縱向鋼筋采用 HRB335級(jí)鋼筋，箍筋采用 HPB235級(jí)鋼筋，均布荷載在梁支座邊緣產(chǎn)生的最大剪力設(shè)計(jì)值為 250kN。 ② 若由于施工原因，混凝土強(qiáng)度等級(jí)僅達(dá)到 C20 級(jí) ， C20 級(jí) 混凝土 /cf N mm? 。236 0 /yyf f N m m?? ， C25 級(jí)混凝土 211 .9 /cf N mm? ， 21520sA mm? 。 ① 混凝土強(qiáng)度等級(jí)為 C25； ② 若由于施工原因，混凝土強(qiáng)度等級(jí)僅達(dá)到 C20級(jí)。試配置截面鋼筋。 已知： 2/ mmNft ? ， 2/300 mmNf yv ? ， h0=465mm 010 hsnAfbhfV svyvtu ?? 解： （ 1）計(jì)算所能承擔(dān)的剪力 010 hsnAfbhfV svyvtu ?? 465150 ????????? N132025? （ 2） 判斷斜截面所能承受的剪力是否安全 KNKNV u ? 不安全。該梁承受的最大剪力設(shè)計(jì)值為 180KN（包括自重），混凝土強(qiáng)度等級(jí) C25，箍筋為 HRB335（ 2/300 mmNf yv ? ），僅配箍筋 2006? 。試求出該梁斜截面所能承受的均布荷載設(shè)計(jì)值 q。 已知： 2/ mmNfc ? ， 2/30 0 mmNff yy ??? ， ?? ， ?b? ， mm35??? ， )(201m a x bbcl bfaM ??? ?? ，)( 02ahfMAys ????? ? ysybcs f AfhbfaA ???? 01 ? 解 ：（ 1）首先計(jì)算受壓鋼筋的 ?sA 為使總用鋼量最小，取混凝土受壓區(qū)高度 0hx b?? )(201m a x bbcl bfaM ??? ?? )( 4 02 0 2 ???????? mmN ??? mKN ?? mKNMMM uu ?????? a x12 )( 02ahfMAys ????? ?= 24 )35440(300 mm??? ? （ 2） 然后計(jì)算受拉鋼筋的 sA ysybcs f AfhbfaA