759 自動彎管機及其電氣設(shè)計【優(yōu)秀含18張CAD圖+文獻翻譯+說明書】
759 自動彎管機及其電氣設(shè)計【優(yōu)秀含18張CAD圖+文獻翻譯+說明書】,優(yōu)秀含18張CAD圖+文獻翻譯+說明書,759,自動彎管機及其電氣設(shè)計【優(yōu)秀含18張CAD圖+文獻翻譯+說明書】,自動,彎管,及其,電氣設(shè)計,優(yōu)秀,優(yōu)良,18,cad,文獻,翻譯,說明書,仿單
開題報告
題 目
自動彎管機裝置及其電器設(shè)計
指導老師
學生姓名
班級學號
專業(yè)
一、課題的意義
現(xiàn)今工業(yè)發(fā)達,無論是哪一種機器設(shè)備、健身器材、家具等幾乎都有結(jié)構(gòu)鋼管,有導管,用以輸油、輸氣、輸液等,而在飛機、汽車及其發(fā)動機,健身器材,家具等等占有相當重要的地位。各種管型品種之多、數(shù)量之大、形狀之復(fù)雜,給導管的加工帶來了不少的困難。對于許多小企業(yè),家庭作坊,或者大企業(yè)中需要配管的場合,如工程機械上的壓力油管,機床廠的液壓管道發(fā)動機的油管健身器材的彎管等等,這些場合可能不需要功能全的彎管機,且加工的管件的難度不高,簡易手動型的彎管機很可能適應(yīng)。這系列彎管機采用手動夾緊,機械彎曲,機器結(jié)構(gòu)簡單,控制元件極少,因此價格上比較容易被用戶接受。
二、課題研究目的和意義
市面上現(xiàn)有的自動彎管機大多數(shù)是液壓的,數(shù)控的,也有機械傳動的,但它們的占地面積較大(長度在2.5~4m之間),價格昂貴(2~5萬元人民幣或更多),然而大多數(shù)用戶需求的是占地面積小價格便宜且使用方便的自動彎管機。
液壓彎管機1-1 數(shù)控彎管機1-2
本文便是朝這方面的用途面設(shè)計的自動彎管機,設(shè)計出一種價格和占地面積使用方便的自動彎管機(長0.9M,寬0.8M,高1.1M,價格9000元人民幣左右),并著手對彎管機的性能進得進一步的強化,使其能彎曲不同口徑或不同的鋼型、采用制動電機以提高彎曲機的彎曲精度。大大的簡化了電器控制系統(tǒng),方便操作。
三、國內(nèi)外自動彎管機概述
彎管機是我國國防和基礎(chǔ)建設(shè)的關(guān)鍵設(shè)備,為我國的經(jīng)濟發(fā)展和國防建設(shè)起到了不可估量的作用。彎管機在前期經(jīng)過了第一步改造,實現(xiàn)了PLC控制、上位計算機監(jiān)控管理、人機友好界面。但現(xiàn)有的操縱控制系統(tǒng)較為落后,不能很好的滿足生產(chǎn)的需要。在此基礎(chǔ)上,迫切需要對彎管機進行第二步改造,將整個操作系統(tǒng)改為中頻感應(yīng)加熱控制,對彎管機的工作過程實現(xiàn)快速、精確控制以提高彎管機的工作效率和加工精度。
? 在電力,石油化工等工業(yè)和天然氣,集中供熱等輸送工程中,需要大量的彎管,彎頭,所以彎管機都作為重要生產(chǎn)設(shè)備之一。它的安全、可靠、高效運行,直接關(guān)系到白動生產(chǎn)線的生產(chǎn)效率和加工質(zhì)量。中頻加熱彎管機具有解熱快,氧化少,解熱均勻,解熱效率高,能保證產(chǎn)品你質(zhì)量等優(yōu)點。
彎管機的PLC控制和編程對彎管起著至關(guān)重要的作用,它的工作性能對整個控制系統(tǒng)都有著重要的影響,所以研究PLC控制和編程極其重要。
? 中頻加熱液壓彎管機組采用了先進的計算機網(wǎng)絡(luò)控制技術(shù),用PLC編程語言及梯形圖形進行邏輯控制連接,采用計算機監(jiān)控系統(tǒng)監(jiān)視和控制現(xiàn)場設(shè)備工作狀態(tài),設(shè)置工藝參數(shù),下的大工藝命令,整機與其他彎管設(shè)備相比:技術(shù)含量高,自動化程度先進,控制精度高,能大大的降低生產(chǎn)成本,提高生產(chǎn)率。
? 控制系統(tǒng)是彎管機的關(guān)鍵組成部分,彎管機的工作性能是系統(tǒng)改造設(shè)計的主要目標。彎管機主要由機械裝置,液壓系統(tǒng),中頻加熱系統(tǒng),PLC控制系統(tǒng),冷卻系統(tǒng)等組成。從系統(tǒng)的觀念考慮機械、電氣和液壓系統(tǒng)之間的匹配問題,得到性能最好的彎管機。
我們已經(jīng)是世界上主要的彎管機生產(chǎn)國家之一,但是目前,管道施工應(yīng)用的彎管機基本上都是進口的,國外比較著名的彎管機生產(chǎn)廠家有德國的VIETZ公司和美國的CRC公司。通用的技術(shù)都是利用靜液壓傳動、氣動控制技術(shù)來實現(xiàn)彎管機的彎管操作和控制。國內(nèi)目前仍沒有具備生產(chǎn)大型彎管機設(shè)計和制造能力的廠家。這主要是國內(nèi)整體工業(yè)化程度不高,國產(chǎn)機械本身的加工精度不夠以及專業(yè)人才的匱乏,加之國產(chǎn)鋼材與進口鋼材的差距是導致機械整體質(zhì)量不高的主要原因。
對于彎管機的技術(shù)發(fā)展有了個基本的了解之后,我們能夠更好的發(fā)展我國的彎管機行業(yè)。
四、課題的研究內(nèi)容、方法、手段與步驟
1、研究內(nèi)容
本論文主要是設(shè)計出一種價格和占地面積使用方便的自動彎管機(長0.9M,寬0.8M,高1.1M,價格9000元人民幣左右),并著手對彎管機的性能進得進一步的強化,使其能彎曲不同口徑或不同的鋼型、采用制動電機以提高彎曲機的彎曲精度。大大的簡化了電器控制系統(tǒng),方便操作。
自動彎管機通用工作流程為:
① 用起重機將管段放置在彎管機工作臺上,操作液壓卷揚機實現(xiàn)管段在工作臺面上位置的準確調(diào)整;
② 利用液壓鉗將管段夾住,操作氣動胎芯自動行走,使其進入管段,并將胎芯撐起;
③ 操作彎管液壓缸,進行管線彎制;
④松開液壓鉗,操作液壓卷揚機,使彎管在工作臺面進行下一個彎管位置的準確調(diào)整;
⑤ 重復(fù)② ~ ④操作,實現(xiàn)下一次彎管動作。一般一根12m 長的管線需要進行15~2O次左右的彎管動作,才能達到最大
l1°的彎曲角度。
2、步驟
①彎管機的基本原理與選擇
彎管機的彎曲原理,在普通情況下有以情二種,即滾彎式與纏繞式。如下圖1、2分別是彎管原理圖。
二者各有優(yōu)缺點。
纏繞式主要用于方管的彎曲其結(jié)構(gòu)復(fù)雜,而滾彎式主要用于圓管彎曲也可用于方管彎曲但沒有纏繞式好,但結(jié)構(gòu)簡單。故本彎管機采用滾彎式。
彎管的步驟大致是:
1.留出第1段直線段長度,并夾緊管子。
2.彎曲。
3.松開夾緊塊,取出管子,使模具復(fù)位。按管形標準樣件在檢驗夾具上檢查管形,并校正。
4.重復(fù)第1步,直至彎完管子為止。
圖1 彎管式彎曲 圖2 纏繞式彎曲
② 工件工藝分析
此工作件采用的直徑為30mm厚為2mm是無縫鋼管做為彎管件,材料為10號鋼,其最小彎曲半徑為60mm。而彎曲件的彎曲半徑為100mm,固其符合加工工藝性。其工件如1-3圖。彎管件要求不能有裂紋,不能有過大的外凸。不能有趨紋。
1、電機選取。
由經(jīng)驗選取彎管機的彎管速度為8r/min。
2、傳動比的計算與各傳動裝置的運動與參數(shù)。
3、皮帶輪與皮帶的計算與選擇由電機轉(zhuǎn)速與功率,確定了采用普通A型皮帶作為傳動帶。
4、蝸輪蝸桿減速箱的計算與選擇
因為蝸輪蝸桿的安裝為蝸桿在蝸輪的側(cè)面所以選用CWS型的蝸輪蝸桿減速器
5、聯(lián)軸器的計算與選擇
由于此聯(lián)軸器承受的力矩相對較大,且顧及性價比軸孔徑的配合關(guān)系且彈性柱銷齒式聯(lián)軸器的結(jié)構(gòu)簡單,制造容易,不需用專用的加工設(shè)備,工作是不需潤滑,維修方便,更換易損件容易迅速,費用低,因此選用彈性柱銷齒式聯(lián)軸器。
6、軸承的選擇
由于彎管機需要一個平穩(wěn)的平臺且軸承同時受有徑向力和軸向力的作用,故不能選用深溝滾子軸承。且軸承受力不大,轉(zhuǎn)速也較低,故可選用圓錐滾子軸承,且可選取外徑較小的以使空間更緊湊和降低成本。選用32912和32918二種圓錐軸承。
7、軸的初步計算與設(shè)計及校核
8、齒輪的計算與設(shè)計
9、大小齒軸前后端蓋及軸承座的結(jié)構(gòu)設(shè)計
10、軸套的結(jié)構(gòu)設(shè)計
11、機身的結(jié)構(gòu)設(shè)計與計算
12、彎管機的主要參數(shù)
③ 擋料架的結(jié)構(gòu)設(shè)計
擋料架在彎管機上的作用主要是用來擋彎曲鋼管時的反力,同時也具有定位的作用。 有如同夾具一般。
由于本彎管機是采用滾彎式的彎管原理,故鋼管與擋料輪的接觸面較不大,故擋料輪的硬度不能比鋼管的硬,故采用黃銅作為擋料輪的材料。
擋料輪的結(jié)構(gòu)主要由擋料輪、擋料軸、擋料輪架、軸承、鍵、軸蓋、擋料座、螺紋桿、手輪等一些組成。
④ 用電器選擇與電路
由于此彎管機采用的是半自動的形式,故采用二個行程開關(guān)和二個交流接觸電器等組成其電路。由于電機的功率為3KW且電壓為380Vh頻率為50Hz的交流電。
故選用行程開關(guān)的型號[1]LX19-131(B),
接觸器型選用[1]CJ-16,2常閉2常開,其工作功率為4KW。
按鈕使用普通型平鈕二個,型號[1]為LA101P-P。
電源開關(guān)選用LW8萬能轉(zhuǎn)換開關(guān)型號[1]為AC21,其工作功率為3.8KW。
短路保護熔斷器選用[1]RL6-25其額定功率為4KW。
過載保護采用[1]JRS1-25/F系列熱繼電器JRS1-25/F其控制功率為380*3=1124W,因為有二根線所以總功率為1124*3=3372W故合適。
電源線采用[1]BV4(B)即常用銅芯聚氯乙烯絕緣電線4平方毫米的銅線線芯結(jié)構(gòu)為7*0.85。其額定電壓為600V
其電路設(shè)計如下
,
⑤ 任務(wù)完成的階段安排及時間安排
畢業(yè)設(shè)計(論文)進程安排:
序號 設(shè)計(論文)各階段名稱 日期(教學周)
1 外文資料翻譯 第4周
2 開題報告 第5、6周
3 總體方案 第7~9周
4 設(shè)計說明書 第15周
⑥ 總結(jié)
我們已經(jīng)是世界上主要的彎管機生產(chǎn)國家之一,但是目前,管道施工應(yīng)用的彎管機基本上都是進口的,國外比較著名的彎管機生產(chǎn)廠家有德國的VIETZ公司和美國的CRC公司。通用的技術(shù)都是利用靜液壓傳動、氣動控制技術(shù)來實現(xiàn)彎管機的彎管操作和控制。國內(nèi)目前仍沒有具備生產(chǎn)大型彎管機設(shè)計和制造能力的廠家。這主要是國內(nèi)整體工業(yè)化程度不高,國產(chǎn)機械本身的加工精度不夠以及專業(yè)人才的匱乏,加之國產(chǎn)鋼材與進口鋼材的差距是導致機械整體質(zhì)量不高的主要原因。希望能通過這次設(shè)計對國內(nèi)的機械方面有所了解,為努力發(fā)展中國的機械行業(yè)做出自己的一份貢獻。
指導教師批閱意見
指導教師(簽名): 年 月 日
外文翻譯
結(jié)構(gòu)設(shè)計
結(jié)構(gòu)設(shè)計
Augustine J.Fredrich
摘要:結(jié)構(gòu)設(shè)計是選擇材料和構(gòu)件類型,大小和形狀以安全有用的樣式承擔荷載。一般說來,結(jié)構(gòu)設(shè)計暗指結(jié)構(gòu)物如建筑物和橋或是可移動但有剛性外殼如船體和飛機框架的工廠穩(wěn)定性。設(shè)計的移動時彼此相連的設(shè)備(連接件),一般被安排在機械設(shè)計領(lǐng)域。
關(guān)鍵詞:結(jié)構(gòu)設(shè)計 ; 結(jié)構(gòu)分析 ; 結(jié)構(gòu)方案 ; 工程要求
Abstract: Structure design is the selection of materials and member type ,size, and configuration to carry loads in a safe and serviceable fashion .In general ,structural design implies the engineering of stationary objects such as buildings and bridges ,or objects that maybe mobile but have a rigid shape such as ship hulls and aircraft frames. Devices with parts planned to move with relation to each other(linkages) are generally assigned to the area of mechanical .
Key words: Structure Design ; Structural analysis ;structural scheme ; Project requirements
Structure Design
Structural design involved at least five distinct phases of work: project requirements, materials, structural scheme, analysis, and design. For unusual structures or materials a six phase, testing, should be included. These phases do not proceed in a rigid progression , since different materials can be most effective in different schemes , testing can result in change to a design , and a final design is often reached by starting with a rough estimated design , then looping through several cycles of analysis and redesign . Often, several alternative designs will prove quite close in cost, strength, and serviceability. The structural engineer, owner, or end user would then make a selection based on other considerations.
Project requirements. Before starting design, the structural engineer must determine the criteria for acceptable performance. The loads or forces to be resisted must be provided. For specialized structures, this may be given directly, as when supporting a known piece of machinery, or a crane of known capacity. For conventional buildings, buildings codes adopted on a municipal, county , or , state level provide minimum design requirements for live loads (occupants and furnishings , snow on roofs , and so on ). The engineer will calculate dead loads (structural and known, permanent installations ) during the design process.
For the structural to be serviceable or useful , deflections must also be kept within limits ,since it is possible for safe structural to be uncomfortable “bounce” Very tight deflection limits are set on supports for machinery , since beam sag can cause drive shafts to bend , bearing to burn out , parts to misalign , and overhead cranes to stall . Limitations of sag less than span /1000 ( 1/1000 of the beam length ) are not uncommon . In conventional buildings, beams supporting ceilings often have sag limits of span /360 to avoid plaster cracking, or span /240 to avoid occupant concern (keep visual perception limited ). Beam stiffness also affects floor “bounciness,” which can be annoying if not controlled. In addition , lateral deflection , sway , or drift of tall buildings is often held within approximately height /500 (1/500 of the building height ) to minimize the likelihood of motion discomfort in occupants of upper floors on windy days .
Member size limitations often have a major effect on the structural design. For example, a certain type of bridge may be unacceptable because of insufficient under clearance for river traffic, or excessive height endangering aircraft. In building design, ceiling heights and floor-to-floor heights affect the choice of floor framing. Wall thicknesses and column sizes and spacing may also affect the serviceability of various framing schemes.
Materials selection. Technological advances have created many novel materials such as carbon fiber and boron fiber-reinforced composites, which have excellent strength, stiffness, and strength-to-weight properties. However, because of the high cost and difficult or unusual fabrication techniques required , they are used only in very limited and specialized applications . Glass-reinforced composites such as fiberglass are more common, but are limited to lightly loaded applications. The main materials used in structural design are more prosaic and include steel, aluminum, reinforced concrete, wood , and masonry .
Structural schemes. In an actual structural, various forces are experienced by structural members , including tension , compression , flexure (bending ), shear ,and torsion (twist) . However, the structural scheme selected will influence which of these forces occurs most frequently, and this will influence the process of materials selection.
Tension is the most efficient way to resist applied loads ,since the entire member cross section is acting to full capacity and bucking is not a concern . Any tension scheme must also included anchorages for the tension members . In a suspension bridge , for example ,the anchorages are usually massive dead weights at the ends of the main cables . To avoid undesirable changes in geometry under moving or varying loads , tension schemes also generally require stiffening beams or trusses.
Compression is the next most efficient method for carrying loads . The full member cross section is used ,but must be designed to avoid bucking ,either by making the member stocky or by adding supplementary bracing . Domed and arched buildings ,arch bridges and columns in buildings frames are common schemes . Arches create lateral outward thrusts which must be resisted . This can be done by designing appropriate foundations or , where the arch occurs above the roadway or floor line , by using tension members along the roadway to tie the arch ends together ,keeping them from spreading . Compression members weaken drastically when loads are not applied along the member axis , so moving , variable , and unbalanced loads must be carefully considered.
Schemes based on flexure are less efficient than tension and compression ,since the flexure or bending is resisted by one side of the member acting in tension while the other side acts in compression . Flexural schemes such as beams , girders , rigid frames , and moment (bending ) connected frames have advantages in requiring no external anchorages or thrust restrains other than normal foundations ,and inherent stiffness and resistance to moving ,variable , and unbalanced loads .
Trusses are an interesting hybrid of the above schemes . They are designed to resist loads by spanning in the manner of a flexural member, but act to break up the load into a series of tension and compression forces which are resisted by individually designed tension and have excellent stiffness and resistance to moving and variable loads . Numerous member-to-member connections, supplementary compression braces ,and a somewhat cluttered appearance are truss disadvantages .
Plates and shells include domes ,arched vaults ,saw tooth roofs , hyperbolic paraboloids , and saddle shapes .Such schemes attempt to direct all force along the plane of the surface ,and act largely in shear . While potentially very efficient ,such schemes have very strict limitations on geometry and are poor in resisting point ,moving , and unbalanced loads perpendicular to the surface.
Stressed-skin and monologue construction uses the skin between stiffening ribs ,spars ,or columns to resist shear or axial forces . Such design is common in airframes for planes and rockets, and in ship hulls . it has also been used to advantage in buildings. Such a design is practical only when the skin is a logical part of the design and is never to be altered or removed .
For bridges , short spans are commonly girders in flexure . As spans increase and girder depth becomes unwieldy , trusses are often used ,as well as cablestayed schemes .Longer spans may use arches where foundation conditions ,under clearance ,or headroom requirements are favorable .The longest spans are handled exclusively by suspension schemes ,since these minimize the crucial dead weight and can be erected wire by wire .
For buildings, short spans are handled by slabs in flexure .As spans increase, beams and girders in flexure are used . Longer spans require trusses ,especially in industrial buildings with possible hung loads . Domes ,arches , and cable-suspended and air –supported roofs can be used over convention halls and arenas to achieve clear areas .
Structural analysis . Analysis of structures is required to ensure stability (static equilibrium ) ,find the member forces to be resisted ,and determine deflections . It requires that member configuration , approximate member sizes ,and elastic modulus ; linearity ; and curvature and plane sections . Various methods are used to complete the analysis .
Final design . once a structural has been analyzed (by using geometry alone if the analysis is determinate , or geometry plus assumed member sizes and materials if indeterminate ), final design can proceed . Deflections and allowable stresses or ultimate strength must be checked against criteria provided either by the owner or by the governing building codes . Safety at working loads must be calculated . Several methods are available ,and the choice depends on the types of materials that will be used .
Pure tension members are checked by dividing load by cross-section area .Local stresses at connections ,such as bolt holes or welds ,require special attention . Where axial tension is combined with bending moment ,the sum of stresses is compared to allowance levels . Allowable : stresses in compression members are dependent on the strength of material, elastic modulus ,member slenderness ,and length between bracing points . Stocky members are limited by materials strength ,while slender members are limited by elastic bucking .
Design of beams can be checked by comparing a maximum bending stress to an allowable stress , which is generally controlled by the strength of the material, but may be limited if the compression side of the beam is not well braced against bucking .
Design of beam-columns ,or compression members with bending moment ,must consider two items . First ,when a member is bowed due to an applied moment ,adding axial compression will cause the bow to increase .In effect ,the axial load has magnified the original moment .Second ,allowable stresses for columns and those for beams are often quite different .
Members that are loaded perpendicular to their long axis, such as beams and beam-columns, also must carry shear. Shear stresses will occur in a direction to oppose the applied load and also at right angles to it to tie the various elements of the beam together. They are compared to an allowable shear stress. These procedures can also be used to design trusses, which are assemblies of tension and compression members. Lastly, deflections are checked against the project criteria using final member sizes.
Once a satisfactory scheme has been analyzed and designed to be within project criteria, the information must be presented for fabrication and construction. This is commonly done through drawings, which indicate all basic dimensions, materials, member sizes, the anticipated loads used in design, and anticipated forces to be carried through connections.
結(jié)構(gòu)設(shè)計
結(jié)構(gòu)設(shè)計包含至少5個不同方面的工作:工程要求,材料,結(jié)構(gòu)方案,分析和設(shè)計。對于不一般的結(jié)構(gòu)或材料,又包含一個方面:試驗。這些方面不是嚴格按步驟進行,因為不同材料在不同方案大多數(shù)是有效的,試驗會導致設(shè)計變更,最終設(shè)計由初步估計設(shè)計開始,然后經(jīng)過分析和再設(shè)計幾個循環(huán)后完成。通常,可替代的設(shè)計證明在費用,強度和使用性上十分接近。結(jié)構(gòu)工程師,業(yè)主或最后住戶基于其它的考慮選擇一種。
工程要求。在開始設(shè)計前,結(jié)構(gòu)工程師必須決定容易接受的執(zhí)行標準。必須提供承擔的荷載或力。對于一些專門結(jié)構(gòu),當支持一臺已知載重的機器或起重機時,這可能直接給出,對于普通建筑物,采用市政,縣,州的建筑規(guī)范,提供了設(shè)計所需活載(人群荷載和設(shè)備,屋頂雪荷載,等等)的最小值。工程師將計算出設(shè)計期間的恒載(結(jié)構(gòu)和已知永久性設(shè)備)。
對要正常使用的結(jié)構(gòu),也必須控制其撓度,因為安全的結(jié)構(gòu)可能會存在令人不安的振動。機器的支座有嚴格的變形限制,因為梁下沉會導致驅(qū)動軸彎曲,燒毀,部件錯位和上面的吊車熄火。撓度限制在跨度/1000 (梁長的1/1000)以下是很普通的。在傳統(tǒng)建筑里,支持板的梁撓度限制在跨度1/360以避免粉刷開裂或跨度1/240以避免人的擔憂(保持在可感知的變動范圍內(nèi))。梁的剛度也影響板“振動”,如果不能控制會令人很頭疼。另外,高層建筑的側(cè)面變形,位移或搖擺通常限定在高度/500(建筑物高度的1/500)里,把在有風的日子里上面樓層的人移動的不舒服降到最小。構(gòu)件尺寸在結(jié)構(gòu)設(shè)計里起主要作用。例如,由于下面留作水上交通的凈空不夠或過高威脅到飛機的特定類型的橋是不可接受的。在建筑設(shè)計里,天花板高度和樓板之間高度影響樓板框架的選擇。墻厚和柱子尺寸和跨度也影響不同框架方案的適用性。
選擇材料。技術(shù)的進步創(chuàng)造了許多新材料,如碳纖維加強復(fù)合材料和硼纖維加強復(fù)合材料,它們都具有極好的強度,剛度和強度重量比特性。然而,由于費用高和非通常的制造要求,它們僅用在有限特殊領(lǐng)域。強化玻璃合成物如玻璃纖維是很普遍,但被限制應(yīng)用在小荷載情況下。用在結(jié)構(gòu)設(shè)計上的主要材料更多是普通的,包括鋼材,鋁,鋼筋混凝土,木材,砌體。
結(jié)構(gòu)方案。在一個實際方案里,結(jié)構(gòu)構(gòu)件承擔很多力,包括拉,壓,彎,剪和扭。然而所選擇的方案將會影響這些力產(chǎn)生的概率,也會影響材料選擇過程。
抗拉是有效的承擔荷載的方法,整個構(gòu)件的橫截面性能得到發(fā)揮,并且不涉及到彎曲變形。任何抗拉方案必須也對抗拉構(gòu)件的錨固。例如,在懸索橋里,錨固體通常是位于主要繩索尾段的強大自重。為了避免在荷載移動或變形時有不期望的幾何變形,抗拉方案通常要求是剛性梁和桁架。
抗壓是另一個很有效的承擔荷載方法。全部桿件截面發(fā)揮了作用,但是設(shè)計時必須避免彎曲,或者是做成粗短構(gòu)件或者是增加附加支撐。圓頂和拱形建筑,拱橋和柱是很普遍的建筑方案。拱產(chǎn)生了必須抵擋住的水平外推力。這靠設(shè)計合適的基礎(chǔ)或建在車道或樓板的上面的拱解決,靠沿著車道用抗拉構(gòu)件把兩端的拱連接起來,阻止他們拉開。當荷載不是作用在構(gòu)件軸線上時,抗壓構(gòu)件顯著地被削弱。所以,必須認真考慮移動,變化和不平衡的荷載。
基于受彎的方案的效率比受拉和壓低,因為彎曲是靠構(gòu)件一邊受拉另一邊受壓來抵抗。受彎方案如主梁,次梁,剛架和受彎框架在外部錨固或推力限制,與一般基礎(chǔ)不同,靠內(nèi)部剛度阻擋可移動,變化和不平衡的荷載的情況下有利。
桁架是上面方案的混合體。它們設(shè)計成荷載橫跨在受彎構(gòu)件上,但是分解成一系列拉力和壓力,由抗拉和抗壓構(gòu)件承擔。桁架方案設(shè)計時不需要特殊錨固或推力的限制,并且有很好的剛度抵抗移動或變化的荷載。大量的構(gòu)件之間連結(jié)和抗壓構(gòu)件的附加支撐,看起來有點雜亂,這就是桁架的不利處。
板和殼包括圓頂,拱頂,有齒屋頂,雙曲拋物面和馬鞍形。這樣的方案把所有的力直接作用在平板表面并且作用有巨大的剪力。盡管可能效率很高,但是這樣的方案對幾何有嚴格的限制,并且在移動,和不平衡垂直作用在表面的荷載的能力很弱。
薄殼結(jié)構(gòu)和硬殼結(jié)構(gòu)利用加勁肋,梁之間的殼板抵抗剪力和軸向力。這樣的設(shè)計在飛機機體和火箭,船體方面很普遍。它在建筑方面也是有利的。這樣的設(shè)計僅僅在殼是設(shè)計的邏輯部分并且永遠不會被替代和移除時才實際些。
對于橋梁,短跨是很普遍受彎的梁。當跨度增加和梁高變得很大時,通常用桁架和斜拉結(jié)構(gòu)。更長跨時也許用拱,要考慮基礎(chǔ)條件和凈空要求。最長的跨靠懸索方案處理,因為這可把關(guān)鍵性的自重降到最小并且能索連索地建造起來。
對于橋,短跨靠板承擔彎矩。當跨度增加時,主梁和次梁被用來承擔彎曲。更長的跨要求用桁架,尤其是在工業(yè)建筑有吊車荷載時,圓頂,拱和懸索和充氣屋頂被用在傳統(tǒng)的大廳和競技場里以獲得凈面積。
結(jié)構(gòu)分析。結(jié)構(gòu)分析要求確定穩(wěn)定性(靜力平衡),構(gòu)件承擔的力和變形。它需要構(gòu)件形狀,大概尺寸,已知或假設(shè)的材料特性。分析包括:平衡,應(yīng)力,應(yīng)變和彈性模量,線形,塑性和彎曲和板截面。很多方法可以完成分析過程。
最終設(shè)計。一旦結(jié)構(gòu)分析完成(如果分析是正確的,只用幾何方法;反之附加構(gòu)件尺寸和材料假設(shè))。最終設(shè)計可以進行,必須對照業(yè)主或政府建筑規(guī)范標準來檢查變形和允許應(yīng)力或極限強度。必須計算工作荷載下的安全性。一般方法是可行的,依據(jù)所使用的材料類型做出選擇。
純抗拉構(gòu)件檢查橫截面應(yīng)力。特別注意螺栓孔或焊接處的應(yīng)力。拉彎構(gòu)件中,用應(yīng)力之和與分析應(yīng)力作比。受壓構(gòu)件中的允許應(yīng)力取決于構(gòu)件強度,彈性模量,長細比和支點間距離。粗短構(gòu)件由材料強度決定,然而長細構(gòu)件由彈性彎曲決定。
梁的設(shè)計由對于最大彎曲應(yīng)力和允許應(yīng)力來檢驗,通常由材料強度控制,但是如果受壓一邊沒有側(cè)向支撐就會被限制。
梁,柱或有彎矩的受壓構(gòu)件的設(shè)計必須考慮兩項。首先,當構(gòu)件由于承受彎矩而彎曲時,軸力會增加彎曲量,實際上,軸壓放大了原始彎矩。其次,對于柱和梁的允許應(yīng)力是不同的。
承受垂直于長軸的荷載的構(gòu)件。如梁和梁——柱,也必須承擔剪力。剪應(yīng)力和荷載的方向相反并且在其右邊,把梁的不同部分連接起來。它們與允許剪應(yīng)力作對比。這些步驟也能用來設(shè)計由受拉和受壓構(gòu)件組成的桁架。最后,用工程標準檢驗變形,使用最后的構(gòu)件。
一旦被分析和在工程標準內(nèi)的設(shè)計方案是令人滿意的,必須提出制造和建立信息。通過作圖,指明所以基本尺寸,材料和構(gòu)件大小。設(shè)計中預(yù)期荷載和節(jié)點承擔的預(yù)期力。
收藏