每年暑期，故宮游人如織。作為我國優秀傳統建筑文化的代表，紫禁城古建筑有著諸多吸引國內外游客的魅力，其中的典型特色之一就是斗拱。斗拱是我國特有的古建筑組成部分，是位于柱頂之上、屋檐之下的由斗形、弓形的木構件在縱橫方向搭扣連接，而后在豎向又層層疊加起來的組合木構件，其外形猶如撐開的傘。我國古建筑學家梁思成先生曾說：“斗拱在中國建筑(zhu)上的地位，猶(you)柱(zhu)(zhu)飾之(zhi)(zhi)于希臘羅馬建筑(zhu)；斗(dou)拱之(zhi)(zhi)變化(hua)，謂為中國建筑(zhu)之(zhi)(zhi)變化(hua)，亦未嘗不(bu)可，猶(you)柱(zhu)(zhu)飾之(zhi)(zhi)影響(xiang)歐洲建筑(zhu)，至(zhi)為重(zhong)大。”

　斗(dou)拱源自(zi)高大宮(gong)殿(dian)屋頂(ding)出檐(yan)深遠的(de)(de)(de)要(yao)求(qiu)。早期的(de)(de)(de)宮(gong)殿(dian)建筑往往采用斜撐的(de)(de)(de)木柱(zhu)來支撐寬大的(de)(de)(de)屋檐(yan)，斜撐分(fen)別設于屋檐(yan)的(de)(de)(de)前后方(fang)(fang)。而為(wei)了(le)(le)避免落地的(de)(de)(de)斜撐受(shou)雨水(shui)侵蝕，其下支點便離開(kai)了(le)(le)地面(mian)，稱為(wei)短斜撐，并(bing)隨(sui)著(zhu)審美(mei)需求(qiu)逐漸(jian)被彎曲的(de)(de)(de)木料替代，形(xing)(xing)成(cheng)了(le)(le)今天斗(dou)拱的(de)(de)(de)橫向重要(yao)構件——翹。同時，為(wei)了(le)(le)增(zeng)強柱(zhu)頂(ding)部位支撐屋檐(yan)的(de)(de)(de)強度，柱(zhu)頂(ding)之上(shang)又(you)增(zeng)加了(le)(le)斗(dou)形(xing)(xing)木塊，木塊上(shang)方(fang)(fang)沿(yan)著(zhu)屋檐(yan)方(fang)(fang)向疊(die)加長(chang)方(fang)(fang)形(xing)(xing)的(de)(de)(de)墊木，這些長(chang)方(fang)(fang)形(xing)(xing)的(de)(de)(de)墊木因審美(mei)需要(yao)逐漸(jian)變成(cheng)弓形(xing)(xing)，形(xing)(xing)成(cheng)了(le)(le)今天斗(dou)拱縱向的(de)(de)(de)重要(yao)構件——拱。

　紫禁城古(gu)建筑的斗(dou)拱(gong)(gong)類型很豐富，如位(wei)于(yu)兩根立柱之(zhi)間的斗(dou)拱(gong)(gong)稱(cheng)為平身科斗(dou)拱(gong)(gong)，位(wei)于(yu)柱頂之(zhi)上(shang)的斗(dou)拱(gong)(gong)為柱頭科斗(dou)拱(gong)(gong)，位(wei)于(yu)建筑四個轉(zhuan)角部位(wei)的斗(dou)拱(gong)(gong)稱(cheng)為角科斗(dou)拱(gong)(gong)等。斗(dou)拱(gong)(gong)的初(chu)始功能(neng)是支(zhi)撐屋檐，并把屋頂的重(zhong)量往下傳遞給柱子。其歷史(shi)發展過程是由(you)構(gou)造簡(jian)單到復雜(za)，功能(neng)由(you)純粹的支(zhi)撐到集建筑力(li)學、美學于(yu)一體。

　紫(zi)禁城古建筑的斗(dou)(dou)拱(gong)(gong)(gong)(gong)(gong)體(ti)現了造型之美。斗(dou)(dou)拱(gong)(gong)(gong)(gong)(gong)在(zai)(zai)屋檐(yan)之下(xia)，整體(ti)排列有序，富(fu)有節(jie)奏(zou)和(he)(he)韻律變化(hua)，不同(tong)類型的斗(dou)(dou)拱(gong)(gong)(gong)(gong)(gong)在(zai)(zai)同(tong)一高度(du)范圍排列規則有序，由下(xia)至上(shang)尺寸統一逐漸增(zeng)大，各斗(dou)(dou)拱(gong)(gong)(gong)(gong)(gong)出踩尺寸相(xiang)同(tong)，斗(dou)(dou)拱(gong)(gong)(gong)(gong)(gong)外(wai)形的曲線整齊劃一、弧度(du)優(you)美，給(gei)(gei)人以(yi)極強的藝術感(gan)和(he)(he)節(jie)奏(zou)感(gan)。斗(dou)(dou)拱(gong)(gong)(gong)(gong)(gong)的造型之美還(huan)體(ti)現在(zai)(zai)均勻對稱(cheng)性(xing)，各個(ge)構件高度(du)、寬度(du)基本(ben)相(xiang)同(tong)，僅在(zai)(zai)長度(du)及外(wai)型上(shang)根(gen)據(ju)整體(ti)需要而有不同(tong)差(cha)別(bie)：一方(fang)面斗(dou)(dou)拱(gong)(gong)(gong)(gong)(gong)的正立(li)面，其左右兩側的構件種類和(he)(he)數(shu)量對稱(cheng)布(bu)置；另一方(fang)面，斗(dou)(dou)拱(gong)(gong)(gong)(gong)(gong)側立(li)面，以(yi)正心枋為中心，斗(dou)(dou)拱(gong)(gong)(gong)(gong)(gong)向內外(wai)出挑的踩數(shu)相(xiang)同(tong)。上(shang)述均勻、對稱(cheng)的布(bu)置形式(shi)給(gei)(gei)人以(yi)舒適、愉悅的感(gan)覺(jue)。

　不僅(jin)如(ru)此，斗(dou)拱(gong)在造型上(shang)還有統(tong)一協調(diao)之(zhi)美。各構件截面(mian)形(xing)狀統(tong)一，均為(wei)方形(xing)或者矩形(xing)；側(ce)立面(mian)外形(xing)統(tong)一，均猶如(ru)倒立的(de)三角形(xing)；斗(dou)拱(gong)位置統(tong)一，均位于(yu)柱頂之(zhi)上(shang)、屋(wu)(wu)檐(yan)之(zhi)下，這種(zhong)統(tong)一性在視(shi)覺上(shang)給人以抽象的(de)整體(ti)之(zhi)美。斗(dou)拱(gong)整體(ti)與上(shang)部傾(qing)斜的(de)屋(wu)(wu)檐(yan)、下部垂直的(de)柱子形(xing)成(cheng)完美過渡，既(ji)能(neng)反(fan)映屋(wu)(wu)架(jia)簡潔明確的(de)特(te)征，又可體(ti)現斗(dou)拱(gong)自身(shen)優美的(de)造型。

　不僅(jin)具有(you)建(jian)筑(zhu)之美(mei)，紫禁城斗(dou)(dou)拱運(yun)用(yong)的(de)(de)(de)(de)另一(yi)(yi)(yi)個重(zhong)(zhong)(zhong)要特征，是(shi)其中(zhong)蘊含(han)了(le)豐富的(de)(de)(de)(de)力學(xue)智慧(hui)。斗(dou)(dou)拱由很(hen)多小(xiao)尺(chi)寸的(de)(de)(de)(de)木構(gou)(gou)件(jian)在水平(ping)和豎(shu)向(xiang)(xiang)拼(pin)插、疊加而成。盡管這(zhe)些木構(gou)(gou)件(jian)尺(chi)寸很(hen)小(xiao)，但(dan)當它們(men)組成一(yi)(yi)(yi)個斗(dou)(dou)拱整體時，就(jiu)會(hui)產生(sheng)巨大(da)(da)的(de)(de)(de)(de)力量(liang)。在一(yi)(yi)(yi)般情況(kuang)下，斗(dou)(dou)拱位于屋(wu)(wu)(wu)檐的(de)(de)(de)(de)下方(fang)(fang)，承(cheng)擔(dan)整個屋(wu)(wu)(wu)頂(ding)的(de)(de)(de)(de)重(zhong)(zhong)(zhong)量(liang)，并(bing)把該重(zhong)(zhong)(zhong)量(liang)向(xiang)(xiang)下傳遞給額枋、柱子。紫禁城古建(jian)筑(zhu)屋(wu)(wu)(wu)頂(ding)有(you)著(zhu)厚厚的(de)(de)(de)(de)泥背層，但(dan)能(neng)夠(gou)被(bei)斗(dou)(dou)拱輕松承(cheng)擔(dan)，且(qie)斗(dou)(dou)拱不會(hui)產生(sheng)破壞，可反映(ying)斗(dou)(dou)拱有(you)很(hen)好的(de)(de)(de)(de)豎(shu)向(xiang)(xiang)承(cheng)載(zai)能(neng)力。這(zhe)種(zhong)良好豎(shu)向(xiang)(xiang)承(cheng)載(zai)能(neng)力主要有(you)兩方(fang)(fang)面原(yuan)因：一(yi)(yi)(yi)方(fang)(fang)面，盡管紫禁城古建(jian)筑(zhu)屋(wu)(wu)(wu)頂(ding)重(zhong)(zhong)(zhong)量(liang)很(hen)大(da)(da)，但(dan)是(shi)這(zhe)個重(zhong)(zhong)(zhong)量(liang)由多個斗(dou)(dou)拱承(cheng)擔(dan)，每(mei)個斗(dou)(dou)拱實際上(shang)承(cheng)擔(dan)的(de)(de)(de)(de)屋(wu)(wu)(wu)頂(ding)重(zhong)(zhong)(zhong)量(liang)較(jiao)小(xiao)，這(zhe)相當于對屋(wu)(wu)(wu)頂(ding)重(zhong)(zhong)(zhong)量(liang)進行了(le)分解(jie)；另一(yi)(yi)(yi)方(fang)(fang)面，盡管斗(dou)(dou)拱由大(da)(da)量(liang)的(de)(de)(de)(de)小(xiao)截面尺(chi)寸木構(gou)(gou)件(jian)組成，但(dan)它們(men)數量(liang)眾多，且(qie)每(mei)個構(gou)(gou)件(jian)均可分擔(dan)屋(wu)(wu)(wu)頂(ding)重(zhong)(zhong)(zhong)量(liang)，這(zhe)樣(yang)一(yi)(yi)(yi)來，傳到(dao)斗(dou)(dou)拱上(shang)的(de)(de)(de)(de)屋(wu)(wu)(wu)頂(ding)重(zhong)(zhong)(zhong)量(liang)進行了(le)第二次分解(jie)，此時傳到(dao)斗(dou)(dou)拱構(gou)(gou)件(jian)單(dan)體上(shang)的(de)(de)(de)(de)作用(yong)力已經很(hen)小(xiao)了(le)，因而斗(dou)(dou)拱構(gou)(gou)件(jian)單(dan)體不會(hui)產生(sheng)破壞。

　斗(dou)拱(gong)(gong)的(de)(de)力學智慧精華在(zai)(zai)于(yu)它的(de)(de)抗(kang)震(zhen)性能(neng)(neng)(neng)(neng)。無論是(shi)水平向(xiang)還是(shi)豎向(xiang)的(de)(de)地(di)震(zhen)波(bo)，都不(bu)會(hui)造成(cheng)(cheng)斗(dou)拱(gong)(gong)破(po)壞。發生地(di)震(zhen)時(shi)，斗(dou)拱(gong)(gong)的(de)(de)各(ge)個(ge)構(gou)(gou)件之間互相(xiang)摩(mo)擦、擠壓(ya)，并產(chan)生往復運(yun)動(dong)，猶(you)如(ru)(ru)一(yi)個(ge)運(yun)動(dong)的(de)(de)機構(gou)(gou)體系。從能(neng)(neng)(neng)(neng)量(liang)守恒角度(du)講，地(di)震(zhen)波(bo)的(de)(de)能(neng)(neng)(neng)(neng)量(liang)傳(chuan)到斗(dou)拱(gong)(gong)位(wei)置(zhi)時(shi)，主要分成(cheng)(cheng)了2部分能(neng)(neng)(neng)(neng)量(liang)：斗(dou)拱(gong)(gong)的(de)(de)內(nei)能(neng)(neng)(neng)(neng)及斗(dou)拱(gong)(gong)的(de)(de)動(dong)能(neng)(neng)(neng)(neng)，斗(dou)拱(gong)(gong)內(nei)能(neng)(neng)(neng)(neng)即(ji)自身產(chan)生開裂破(po)壞的(de)(de)根本原因，內(nei)能(neng)(neng)(neng)(neng)越大(da)(da)，斗(dou)拱(gong)(gong)破(po)壞越嚴重(zhong)。然而(er)斗(dou)拱(gong)(gong)能(neng)(neng)(neng)(neng)量(liang)的(de)(de)另(ling)一(yi)個(ge)組(zu)成(cheng)(cheng)部分即(ji)動(dong)能(neng)(neng)(neng)(neng)占的(de)(de)比例遠(yuan)大(da)(da)于(yu)自身的(de)(de)內(nei)能(neng)(neng)(neng)(neng)，其原因在(zai)(zai)于(yu)每個(ge)斗(dou)拱(gong)(gong)由上百(bai)個(ge)小構(gou)(gou)件組(zu)成(cheng)(cheng)，它們猶(you)如(ru)(ru)機器的(de)(de)零件一(yi)樣，在(zai)(zai)地(di)震(zhen)作(zuo)用下不(bu)斷產(chan)生各(ge)種(zhong)運(yun)動(dong)，耗散了大(da)(da)量(liang)的(de)(de)地(di)震(zhen)能(neng)(neng)(neng)(neng)量(liang)，從而(er)使得斗(dou)拱(gong)(gong)內(nei)能(neng)(neng)(neng)(neng)的(de)(de)比例很小，因而(er)斗(dou)拱(gong)(gong)在(zai)(zai)地(di)震(zhen)作(zuo)用下幾(ji)乎(hu)不(bu)會(hui)產(chan)生破(po)壞。事實上，大(da)(da)量(liang)的(de)(de)古建震(zhen)害勘查結果表明，斗(dou)拱(gong)(gong)在(zai)(zai)地(di)震(zhen)作(zuo)用下一(yi)般保存完好(hao)。

　不(bu)僅(jin)如(ru)此，地(di)震作用下(xia)，斗(dou)(dou)拱(gong)(gong)還能(neng)產(chan)生自動恢復(fu)(fu)功能(neng)，猶如(ru)不(bu)倒翁(weng)一(yi)樣，其原(yuan)因在(zai)于(yu)斗(dou)(dou)拱(gong)(gong)特(te)(te)殊的(de)(de)構(gou)造(zao)特(te)(te)征(zheng)。斗(dou)(dou)拱(gong)(gong)整體(ti)構(gou)造(zao)特(te)(te)點是上部(bu)體(ti)積(ji)大(da)但(dan)構(gou)件(jian)單(dan)體(ti)截面尺(chi)寸小(xiao)、下(xia)部(bu)體(ti)積(ji)小(xiao)但(dan)構(gou)件(jian)單(dan)體(ti)截面尺(chi)寸大(da)，其中截面尺(chi)寸最大(da)的(de)(de)為方(fang)(fang)形(xing)的(de)(de)坐(zuo)(zuo)斗(dou)(dou)，位(wei)于(yu)斗(dou)(dou)拱(gong)(gong)的(de)(de)最底層。這(zhe)種(zhong)構(gou)造(zao)特(te)(te)征(zheng)使(shi)得：一(yi)方(fang)(fang)面斗(dou)(dou)拱(gong)(gong)的(de)(de)重心位(wei)于(yu)斗(dou)(dou)拱(gong)(gong)的(de)(de)下(xia)方(fang)(fang)，斗(dou)(dou)拱(gong)(gong)猶如(ru)一(yi)個(ge)矮(ai)胖的(de)(de)人，在(zai)水平地(di)震力（推(tui)拉力）作用下(xia)盡管產(chan)生搖(yao)擺(bai)，但(dan)是不(bu)易傾(qing)覆；另一(yi)方(fang)(fang)面坐(zuo)(zuo)斗(dou)(dou)的(de)(de)截面尺(chi)寸寬大(da)，這(zhe)無疑(yi)增大(da)了斗(dou)(dou)拱(gong)(gong)與(yu)其底部(bu)的(de)(de)接(jie)觸面，斗(dou)(dou)拱(gong)(gong)在(zai)水平地(di)震作用下(xia)產(chan)生搖(yao)擺(bai)時，分別繞(rao)著坐(zuo)(zuo)斗(dou)(dou)兩側的(de)(de)支點進(jin)行(xing)搖(yao)擺(bai)。而(er)在(zai)斗(dou)(dou)拱(gong)(gong)搖(yao)擺(bai)過程中，其上部(bu)屋頂的(de)(de)重量迫(po)使(shi)斗(dou)(dou)拱(gong)(gong)不(bu)斷地(di)復(fu)(fu)位(wei)，因而(er)斗(dou)(dou)拱(gong)(gong)像(xiang)不(bu)倒翁(weng)一(yi)樣，不(bu)斷地(di)來回(hui)擺(bai)動。地(di)震波結(jie)束(shu)后(hou)，斗(dou)(dou)拱(gong)(gong)又(you)恢復(fu)(fu)到(dao)了初始位(wei)置，本身并(bing)未受(shou)到(dao)損害。

　可以認為，紫禁城古建筑斗拱的運(yun)用體現了我國古建(jian)筑的力與(yu)美，是(shi)我國古代工匠(jiang)汗水(shui)與(yu)智慧的結晶。