折疊臂式橋梁檢測(cè)車(chē)的設(shè)計(jì)
折疊臂式橋梁檢測(cè)車(chē)的設(shè)計(jì),折疊臂式橋梁檢測(cè)車(chē)的設(shè)計(jì),折疊,橋梁,檢測(cè),設(shè)計(jì)
存檔編碼：無(wú)無(wú)錫錫太太湖湖學(xué)學(xué)院院 2013 屆屆畢畢業(yè)業(yè)作作業(yè)業(yè)周周次次進(jìn)進(jìn)度度計(jì)計(jì)劃劃、檢檢查查落落實(shí)實(shí)表表 系別：信機(jī)系 班級(jí)：機(jī)械93 學(xué)生姓名：殷曉鋒 課題（設(shè)計(jì)）名稱(chēng)：折疊臂式橋梁檢測(cè)車(chē)的設(shè)計(jì) 開(kāi)始日期：2012年11月12日周次起止日期工作計(jì)劃、進(jìn)度每周主要完成內(nèi)容存在問(wèn)題、改進(jìn)方法指導(dǎo)教師意見(jiàn)并簽字備 注1-32012年11月12日-2012年12月2日查閱相關(guān)資料，完成開(kāi)題報(bào)告按照任務(wù)書(shū)要求查閱論文相關(guān)參考資料，填寫(xiě)畢業(yè)設(shè)計(jì)開(kāi)題報(bào)告書(shū)參考資料不太詳細(xì)，論文中相關(guān)的設(shè)計(jì)結(jié)構(gòu)比較分散，要將各論文中設(shè)計(jì)的部件整合起來(lái)一起研究分析4-102012年12月3日-2013年1月20日指導(dǎo)專(zhuān)業(yè)實(shí)訓(xùn)，要求了解企業(yè)結(jié)構(gòu)進(jìn)入工廠實(shí)習(xí)，了解企業(yè)生產(chǎn)流程初次進(jìn)入工廠實(shí)習(xí)，對(duì)生產(chǎn)結(jié)構(gòu)不太熟悉，要多動(dòng)手做，加強(qiáng)熟悉工作流程112013年2月11日-2月16日查找一篇與論文相關(guān)的學(xué)術(shù)性英文資料，要求是期刊論文查找一篇關(guān)于橋梁檢測(cè)車(chē)的學(xué)術(shù)性英文資料如何查找英文資料還不太清楚，要多加學(xué)習(xí)122013年2月18日-2月23日嚴(yán)格按照要求翻譯英文資料，其中公式必須用公式編輯器輸入翻譯英文資料翻譯中遇到很多專(zhuān)業(yè)術(shù)語(yǔ)，翻譯語(yǔ)句不通順，加強(qiáng)英語(yǔ)練習(xí)，通順語(yǔ)句132013年3月4日-3月8日指導(dǎo)完成總的結(jié)構(gòu)方案設(shè)計(jì)確定折疊臂式橋梁檢測(cè)車(chē)的設(shè)計(jì)方案，整理設(shè)計(jì)思路設(shè)計(jì)思路不夠明確，對(duì)于所要完成的任務(wù)還不是十分清楚，要明確目標(biāo)，設(shè)定計(jì)劃142013年3月4日-3月9日指導(dǎo)繪制裝配圖開(kāi)始繪制折疊臂式橋梁檢測(cè)車(chē)的裝配圖部分圖紙尺寸不全，多查找相關(guān)資料，查找尺寸152013年3月11號(hào)-3月16日完成裝配圖的繪制完成裝配圖的繪制，并檢查修改對(duì)于各部件的裝配關(guān)系不太清楚，要理清各部件間的裝配162013年3月18日-3月23日指導(dǎo)完成部件圖的繪制完成繪制旋轉(zhuǎn)機(jī)結(jié)構(gòu)圖紙部分圖紙尺寸不全，多查找相關(guān)資料，查找尺寸172013年3月25日-3月30日指導(dǎo)完成部件圖的繪制完成伸縮臂的設(shè)計(jì)，并畫(huà)出部件圖紙折疊結(jié)構(gòu)的運(yùn)動(dòng)機(jī)理不清楚，要查閱相關(guān)資料，熟悉折疊運(yùn)動(dòng)機(jī)理182013年4月1日-4月6日完成零件圖的繪制完成回轉(zhuǎn)平臺(tái)的設(shè)計(jì)，并畫(huà)出零件圖紙不知道使用哪種結(jié)構(gòu)最佳，要建立模型，受力分析，確定最佳結(jié)構(gòu)192013年4月8日-4月13日完成零件圖的繪制完成繪制工作斗的設(shè)計(jì)，并畫(huà)出圖紙部分圖紙尺寸不全，多查找相關(guān)資料，估算尺寸202013年4月15日-4月20日完成零件圖的繪制完成液壓系統(tǒng)的設(shè)計(jì)計(jì)算，畫(huà)出零件圖對(duì)液壓系統(tǒng)的設(shè)計(jì)計(jì)算比較生疏，查閱書(shū)籍，按照書(shū)上步驟一步一步設(shè)計(jì)計(jì)算212013年4月22日-4月27日指導(dǎo)說(shuō)明書(shū)初稿寫(xiě)作根據(jù)所下載的資料，構(gòu)思并開(kāi)始寫(xiě)說(shuō)明書(shū)對(duì)各章應(yīng)寫(xiě)哪些內(nèi)容比較模糊，可根據(jù)設(shè)計(jì)的圖紙，著重介紹個(gè)部件222013年4月29日-5月3日指導(dǎo)說(shuō)明書(shū)二稿寫(xiě)作、修改將整篇文章的脈絡(luò)、細(xì)節(jié)加以完善，用詞準(zhǔn)確，不出現(xiàn)病句等。有很多細(xì)節(jié)錯(cuò)誤，將文章再?gòu)?fù)查一邊，避免出現(xiàn)語(yǔ)句上的和細(xì)節(jié)方面的錯(cuò)誤232013年5月6日-5月10指導(dǎo)修改說(shuō)明書(shū)并定稿說(shuō)明書(shū)按照模板進(jìn)行修改格式經(jīng)常出錯(cuò)，耐心修改，要熟練使用word各項(xiàng)功能242013年5月13日-5月18日說(shuō)明書(shū)及相關(guān)資料、圖紙打印裝訂打印說(shuō)明書(shū)和圖紙及相關(guān)資料論文格式嚴(yán)格按照學(xué)校的規(guī)范進(jìn)行修改,完善252013年5月20日-5月25日指導(dǎo)學(xué)生整理資料，準(zhǔn)備答辯整理資料，并熟讀資料，做好充分準(zhǔn)備存在很多細(xì)節(jié)方面的錯(cuò)誤，應(yīng)認(rèn)真檢查并及時(shí)改正 說(shuō)明：1、“工作計(jì)劃、進(jìn)度”、“指導(dǎo)教師意見(jiàn)并簽字”由指導(dǎo)教師填寫(xiě)，“每周主要完成內(nèi)容”，“存在問(wèn)題、改進(jìn)方法”由學(xué)生填寫(xiě)。2、本表由各系妥善歸檔，保存?zhèn)洳?。周次起止日期工作?jì)劃、進(jìn)度每周主要完成內(nèi)容存在問(wèn)題、改進(jìn)方法指導(dǎo)教師意見(jiàn)并簽字備 注無(wú)錫太湖學(xué)院
信 機(jī) 系 機(jī)械工程及自動(dòng)化 專(zhuān)業(yè)
畢 業(yè) 設(shè) 計(jì)論 文 任 務(wù) 書(shū)
一、題目及專(zhuān)題：
1、題目 折疊臂式橋梁檢測(cè)車(chē)的設(shè)計(jì)
2、專(zhuān)題
二、課題來(lái)源及選題依據(jù)
橋梁檢測(cè)車(chē)是一種可以為橋梁檢測(cè)人員在檢測(cè)過(guò)程中提供作業(yè)平臺(tái)，裝備有橋梁檢測(cè)儀器，用于流動(dòng)檢測(cè)和(或)維修作業(yè)的專(zhuān)用汽車(chē)。它可以隨時(shí)移動(dòng)位置，能安全、快速、高效地讓檢測(cè)人員進(jìn)入作業(yè)位置進(jìn)行流動(dòng)檢測(cè)或維修作業(yè)。工作時(shí)不影響交通，而且可以在不收回臂架的情況下慢速行駛。
橋梁檢測(cè)車(chē)技術(shù)含量很高，涉及到機(jī)械、液壓、電子、雷達(dá)、通信等先進(jìn)技術(shù)。具有效率高、安全性好、適應(yīng)性強(qiáng)、功率消耗低等優(yōu)點(diǎn)，適用于特大型公路橋、城市高架橋、鐵路橋、公鐵兩用橋的預(yù)防性檢查和維修作業(yè)，并為操作者在檢測(cè)每一組成部分時(shí)提供安全保障，還可用于環(huán)境險(xiǎn)惡不適合人工檢測(cè)的場(chǎng)合。這種車(chē)輛一般是在二類(lèi)貨車(chē)底盤(pán)基礎(chǔ)上加裝專(zhuān)用工作裝置而成的。
三、本設(shè)計(jì)（論文或其他）應(yīng)達(dá)到的要求：
①完成折疊臂式橋梁檢測(cè)車(chē)的總體方案設(shè)計(jì)；
②完成零部件的選型計(jì)算、結(jié)構(gòu)強(qiáng)度校核；
③熟練掌握有關(guān)計(jì)算機(jī)繪圖軟件，并繪制裝配圖和零件圖紙，折合A0圖紙不少于3張；
④完成設(shè)計(jì)說(shuō)明書(shū)的撰寫(xiě)，并翻譯外文資料1篇。
四、接受任務(wù)學(xué)生：
機(jī)械93 班 姓名 殷曉鋒
五、開(kāi)始及完成日期：
自2012年11月12日 至2013年5月25日
六、設(shè)計(jì)（論文）指導(dǎo)（或顧問(wèn)）：
指導(dǎo)教師 簽名
簽名
簽名
教研室主任
〔學(xué)科組組長(zhǎng)研究所所長(zhǎng)〕 簽名
系主任 簽名
2012年11月12日
無(wú) 錫 太 湖 學(xué) 院
畢業(yè)設(shè)計(jì)（論文）外文資料翻譯
院 （系）： 信 機(jī) 系
專(zhuān) 業(yè)： 機(jī)械工程及自動(dòng)化
班 級(jí)： 機(jī) 械 93
姓 名： 殷 曉 鋒
學(xué) 號(hào)： 0923149
外文出處：
附 件： 1.原文；2.譯文
2013年 5月
編號(hào)
無(wú)錫太湖學(xué)院
畢業(yè)設(shè)計(jì)（論文）
相關(guān)資料
題目： 折疊臂式橋梁檢測(cè)車(chē)的設(shè)計(jì)
信機(jī) 系 機(jī)械工程及自動(dòng)化專(zhuān)業(yè)
學(xué) 號(hào)： 0923110
學(xué)生姓名： 殷曉鋒
指導(dǎo)教師： 黃敏 （職稱(chēng)：副教授 ）
（職稱(chēng)： ）
2013年5月25日
目 錄
一、畢業(yè)設(shè)計(jì)（論文）開(kāi)題報(bào)告
二、畢業(yè)設(shè)計(jì)（論文）外文資料翻譯及原文
三、學(xué)生“畢業(yè)論文（論文）計(jì)劃、進(jìn)度、檢查及落實(shí)表”
四、實(shí)習(xí)鑒定表
無(wú)錫太湖學(xué)院
畢業(yè)設(shè)計(jì)（論文）
開(kāi)題報(bào)告
題目： 折疊臂式橋梁檢測(cè)車(chē)的設(shè)計(jì)
信機(jī) 系 機(jī)械工程及自動(dòng)化 專(zhuān)業(yè)
學(xué) 號(hào)： 0923110
學(xué)生姓名： 殷曉鋒
指導(dǎo)教師： 黃 敏（職稱(chēng)：副教授）
（職稱(chēng)： ）
2012年11月25日
課題來(lái)源
自擬題目
科學(xué)依據(jù)
（1）課題科學(xué)意義
橋梁檢測(cè)車(chē)是一種可以為橋梁檢測(cè)人員在檢測(cè)過(guò)程中提供作業(yè)平臺(tái)，裝備有橋梁檢測(cè)儀器，用于流動(dòng)檢測(cè)和(或)維修作業(yè)的專(zhuān)用汽車(chē)。它可以隨時(shí)移動(dòng)位置，能安全、快速、高效地讓檢測(cè)人員進(jìn)入作業(yè)位置進(jìn)行流動(dòng)檢測(cè)或維修作業(yè)。工作時(shí)不影響交通，而且可以在不收回臂架的情況下慢速行駛。
橋梁檢測(cè)車(chē)技術(shù)含量很高，涉及到機(jī)械、液壓、電子、雷達(dá)、通信等先進(jìn)技術(shù)。具有效率高、安全性好、適應(yīng)性強(qiáng)、功率消耗低等優(yōu)點(diǎn)，適用于特大型公路橋、城市高架橋、鐵路橋、公鐵兩用橋的預(yù)防性檢查和維修作業(yè)，并為操作者在檢測(cè)每一組成部分時(shí)提供安全保障，還可用于環(huán)境險(xiǎn)惡不適合人工檢測(cè)的場(chǎng)合。
這種車(chē)輛一般是在二類(lèi)貨車(chē)底盤(pán)基礎(chǔ)上加裝專(zhuān)用工作裝置而成的。
（2）折疊臂式橋梁監(jiān)測(cè)車(chē)的研究狀況及其發(fā)展前景：
折疊臂式橋梁檢測(cè)車(chē)一般具有以下特點(diǎn)；
①采用機(jī)、電、液、訊一體化技術(shù)，控制系統(tǒng)采用電液比例及自動(dòng)伺服調(diào)平技術(shù)，能精確控制每個(gè)細(xì)微動(dòng)作；
②一般采用一級(jí)伸縮、二級(jí)回轉(zhuǎn)、二級(jí)變幅機(jī)構(gòu)，形成二維空間、6個(gè)自由度的空間運(yùn)動(dòng)體系，工作臂可跨越一定寬度和高度的障礙物，以便順利將工作斗或工作平臺(tái)伸至橋下，安全、快捷地將工作人員和設(shè)備送到橋下幅度允許的任意位置；
③工作斗中加裝先進(jìn)的過(guò)載保護(hù)系統(tǒng)，可實(shí)時(shí)監(jiān)控作業(yè)平臺(tái)負(fù)荷，超載報(bào)警并自動(dòng)限制操作，確保檢測(cè)作業(yè)的安全性，若采用工作平臺(tái)，則需具有自動(dòng)液壓水平調(diào)節(jié)功能，確保工作平穩(wěn)；
④根據(jù)實(shí)際情況在底盤(pán)上加裝支腿穩(wěn)定器，并保證能使整車(chē)在橋下檢修工作狀態(tài)下行駛。
橋梁檢測(cè)作業(yè)車(chē)的發(fā)展適應(yīng)了社會(huì)的需要，市場(chǎng)空間廣闊，但由于技術(shù)含量較高，可靠性、安全性要求較高，而非一般企業(yè)所能生產(chǎn)。國(guó)內(nèi)有條件的專(zhuān)用車(chē)生產(chǎn)廠應(yīng)抓住有利時(shí)機(jī)和機(jī)遇，盡快提高我國(guó)橋梁檢測(cè)車(chē)的技術(shù)水平，降低生產(chǎn)制造成本，提升市場(chǎng)競(jìng)爭(zhēng)力。
研究?jī)?nèi)容
（1） 了解折疊臂式橋梁檢測(cè)車(chē)的工作原理，國(guó)內(nèi)外的研究發(fā)展現(xiàn)狀；
（2） 完成折疊臂式橋梁檢測(cè)車(chē)的上體機(jī)的總體方案設(shè)計(jì)；
（3） 完成零部件的選型計(jì)算、結(jié)構(gòu)強(qiáng)度校核；
（4） 熟練掌握有關(guān)計(jì)算機(jī)繪圖軟件，并繪制裝配圖和零件圖紙，折合A0不少于3張；
（5） 完成設(shè)計(jì)說(shuō)明書(shū)的撰寫(xiě)，并翻譯外文資料1篇。
擬采取的研究方法、技術(shù)路線、實(shí)驗(yàn)方案及可行性分析
研究方法：
通過(guò)參閱借來(lái)的參考資料，并對(duì)折疊臂式橋梁檢測(cè)車(chē)進(jìn)行實(shí)體觀察，認(rèn)真研究上體機(jī)結(jié)構(gòu)，了解折疊臂式橋梁檢測(cè)車(chē)工作原理，與指導(dǎo)老師交流來(lái)完成對(duì)折疊臂式橋梁檢測(cè)車(chē)結(jié)構(gòu)的畢業(yè)設(shè)計(jì)。
技術(shù)路線：
提出任務(wù)分析對(duì)機(jī)器的需求確定任務(wù)要求，完成設(shè)計(jì)任務(wù)書(shū)。方案設(shè)計(jì)階段對(duì)檢測(cè)車(chē)功能進(jìn)行分析提出可能的解決方案，組合幾種可能的方案進(jìn)行評(píng)價(jià)決策，選定最優(yōu)方案該階段目標(biāo)為提出原理性的設(shè)計(jì)方案－原理圖或機(jī)構(gòu)運(yùn)動(dòng)見(jiàn)簡(jiǎn)圖。技術(shù)設(shè)計(jì)階段明確構(gòu)形要求結(jié)構(gòu)化選擇材料決定尺寸，評(píng)價(jià)再?zèng)Q策,確定結(jié)構(gòu)形狀及尺寸，零件設(shè)計(jì)、部件設(shè)計(jì)、上體設(shè)計(jì),該階段完成上體結(jié)構(gòu)、草圖及部件裝配草圖，并繪制出零件圖部件圖總裝圖最后完成技術(shù)文件的編制其中包括編制設(shè)計(jì)計(jì)算說(shuō)明書(shū)、使用說(shuō)明書(shū)、標(biāo)準(zhǔn)明細(xì)表、其他技術(shù)文件等。
技術(shù)可行性：
作為機(jī)械專(zhuān)業(yè)的學(xué)生所常用的必備軟件，CAD、UG軟件。
研究計(jì)劃及預(yù)期成果
研究計(jì)劃：
2012年11月12日-2012年1月20日：按照任務(wù)書(shū)要求查閱論文相關(guān)參考資料，填寫(xiě)畢業(yè)設(shè)計(jì)開(kāi)題報(bào)告書(shū)，并實(shí)訓(xùn)。
2013年2月11日-2013年2月23日：找一篇相關(guān)外文期刊并翻譯。構(gòu)建框架，完成第一章緒論。
2013年3月4日-2013年3月8日：完成總的結(jié)構(gòu)方案設(shè)計(jì)。
2013年3月11日-2013年4月20日：開(kāi)始繪圖，完成裝配圖以及部件圖的繪制。
2013年4月22日-5月3日：著手寫(xiě)說(shuō)明書(shū)初稿，修改，完成初稿。
2013年5月6日-5月10日：修改說(shuō)明書(shū)并定稿，打印，整理資料準(zhǔn)備答辯。
特色或創(chuàng)新之處
（1）主題明確，有針對(duì)性,穩(wěn)定, 易操作, 通用性強(qiáng)。
（2）使用簡(jiǎn)易，功能完善。
已具備的條件和尚需解決的問(wèn)題
（1）技術(shù)條件：整體構(gòu)架基本明確，有電腦，有CAD作圖軟件。
（2）尚未解決的問(wèn)題：技術(shù)還不夠成熟。
指導(dǎo)教師意見(jiàn)
指導(dǎo)教師簽名：
年 月 日
教研室（學(xué)科組、研究所）意見(jiàn)
教研室主任簽名：
年 月 日
系意見(jiàn)
主管領(lǐng)導(dǎo)簽名：
年 月 日
英文原文
An innovative method for remote measurement of minimum vertical underclearance in routine bridge inspection
B. Riveiro a, D.V. Jauregui b, P. Arias c, J. Armesto c, R. Jiang d
a.Department of Materials Engineering, Applied Mechanics and Construction, School of Industrial Engineering, University of Vigo, C.P. 36208, Vigo, Spain
b. Department of Civil Engineering, College of Engineering, New Mexico State University, Las Cruces, NM, USA
c.Department of Natural Resources and Environmental Engineering, School of Mining Engineering, University of Vigo, C.P. 36310, Vigo, Spain
d.Department of Engineering Technology and Surveying Engineering, College of Engineering, New Mexico State University, Las Cruces, NM, USA
Articleinfoabstract
Article history:
Accepted 18 April 2012
Available online 17 May 2012
This paper presents an innovative and low cost procedure for the complete and accurate measurement of minimum vertical underclearance in a safe environment for operators. This procedure draws on the principlesof terrestrial convergent photogrammetry which makes possible the reconstruction of the bridge components and surrounding features in 3D space. Using themeasured 3D coordinates, an algorithm was developed in the Matlab software to calculate the vertical underclearance. Furthermore, a procedure based on 3D curve fitting was developed to estimate the mathematical expression of the beam curve. The resulting methodology is suitable and advantageous for implementation in routine bridge inspection because it provides a more extensive and accurate measurement of vertical underclearance under much safer conditions. In addition, the estimate of the beam equation can be used not only for clearance measurement but also for periodic monitoring of the beam shape over time.
Keywords:Bridge inspection ;Close range photogrammetry ;Vertical underclearance.
1 Introduction
It is true that extensive knowledge of the functional and conservation states of a structure is needed in order to properly schedule its maintenance and ultimately, ensure its preservation. Periodic monitoring of geometry usually plays a key role in the detection of structural anomalies, and in some cases such as stone arch bridges, can aid in preventing collapse due to problems with equilibrium and stability [1]. In the case of modern bridges (mainly composed of concrete or steel), although the diagnosis of their condition state is assessed based primarily on the physical condition of the structural elements, the external shape and geometry also plays a very important role in the overall evaluation. The presence of deterioration, defects, and damages (e.g., impact damage caused by truck collisions, concrete spalls or delaminations, fatigue or shear cracks, section loss) and evidence of irregular movement are the most important parameters considered during a routine bridge inspection, and move advanced tools for their detection and quantification need to be investigated.
Bridge inspection is a key factor in the maintenance and preservation of the civil infrastructure of a country. Many parameters have to be periodically evaluated in order to determine the physical condition of the structure [4–5]. In the bridge management protocol of transportation agencies, there usually exists an initial phase focused on routine inspection, where, by means of quick and simple documentation, the first diagnosis of the current state of the structure is obtained [6–8]. When some evidence of distress about the physical condition or stability of the structure is found in this initial step such as excessive beam sag or support settlement, a special inspection plan should be initiated to perform an in-depth evaluation of the bridge. Currently, there are several basic techniques available to measure irregular bridge movement such as plumb bobs, laser levels, theodolites, and total stations.Horizontal and vertical clearances are important geometric parameters that must be measured to a high level of accuracy during a routine bridge inspection. The acquisition of these dimensions is traditionally accomplished by means of basic contact tools such as tape measures and range poles that lack metric accuracy, and which also require the operators to perform the clearance measurements under dangerous traffic conditions. Fig. 1 illustrates the use of a range pole to measure the minimum vertical underclearance which is the distance from the roadway or railroad track beneath the bridge to the underside of the superstructure . As shown in the figure, measurements are usually taken at discrete points on the bottom surface of the beam to save time and also due to safety concerns. Furthermore, it is difficult to keep the range pole perfectly vertical to obtain an accurate measurement particularly for higher clearances. Consequently, it is possible that the minimum vertical underclearance is not measured accurately at the correct location. There are 116 items of bridge data used by the FHWA to monitor and manage the National Bridge Inventory (NBI) in the United States as given in the Structure Inventory and Appraisal (SI&P) sheet. The data are divided between inventory items that pertain to the permanent conditions of the bridge and appraisal items that pertain to the condition of the bridge component in comparison to current standards . In the SI&P sheet, geometric data are considered inventory items under which the minimum vertical underclearance is item 54. This particular item is coded with 5 digits; the first digit represents the reference feature (highway or railroad beneath structure) and the remaining four digits represent the minimum vertical underclearance (in feet and inches). Underclearance information is used by personnel involved with the permitting of oversize/overweight vehicles and is used in evaluating the sufficiency of a bridge to remain in service (i.e., sufficiency rating). Four separate factors are determined (using 19 of the 116 items reported in the SI&A sheet) to arrive at the sufficiency rating:(1) structural adequacy and safety; (2) serviceability and functional obsolescence; (3) essentiality for public use; and (4) special reductions. Horizontal and vertical underclearances and the deck condition affect the second factor while the superstructure and substructure conditions affect the first factor. The sufficiency rating ranges from 0 to 100% with the latter percentage representing an entirely sufficient bridge. Bridges qualify for replacement when the rating falls below 50% and rehabilitation when the rating falls below 80% . In spite of the simplicity and rapidity in using traditional instruments, the quality of metric results is poor. Surveying techniques offer better quality results in terms of accuracy, but these methods have important limitations for regular use in relation to handling of equipment and the amount of data collected. Terrestrial photogrammetry and laser scanning are two geomatic techniques which have significantly evolved, being more and more used in diverse fields including architecture [9,10]; civil engineering [11–14]; industry[15,16];and archaeology [17,18]. Many investigations show the potential of these new technologies in the field of bridge engineering [19]. From the captured precise 3D geometry of bridges, for example, an improved assessment of the structure can be made [20]. Laser scanning is gaining popularity due to its simplicity in usage and speed of acquisition [21]. A few studies of damage detection in concrete bridges using terrestrial laser scanner data can be found in [22–24]. Similar to traditional surveying equipment, laser scanning presents important limitations for routine inspection work including cost of equipment, necessity for trained operators, and amount of data stored during the bridge survey. Consequently, low cost technologies capable of collecting meaningful and accurate metric data without the need for overly complicated equipment operation and extensive data processing are needed. Close range photogrammetry has several strengths that make it a suitable method for measuring bridge features during a routine inspection such as it utilizes low cost equipment, it is relatively easy to use, and it provides high metric precision. An extensive review of the application of this technique in bridge engineering can be found in [19]. Gonzalez-Aguilera and Gómez-Lahoz [25] present a novel photogrammetric system based on a single image for obtaining the overall geometry of bridges by means of dimensional analysis. Other studies related to bridge monitoring based on photogrammetric methods included those performed by Chang and Ji [26] and Hang et al. [27]. Before new technologies are included in the protocols for metric documentation, they must first be validated. In this context, methodologies of surveying need to be adapted to overcome the existing difficulties in routine bridge inspection. This paper presents an innovative and low cost procedure for the complete and accurate measurement of minimum vertical underclearance in a safe environment for operators. This procedure draws on the principles of terrestrial convergent photogrammetry which makes possible the reconstruction of the bridge components and surrounding features in 3D space.Using the measured 3D coordinates, an algorithm was developed in the Matlab software to calculate the vertical underclearance. Furthermore, a procedure based on 3D curve fitting was developed to estimate the mathematical expression of the beam curve. The resulting methodology is suitable and advantageous for implementation inroutine bridge inspection because it provides a more extensive and accurate measurement of vertical underclearance under much safer conditions. In addition, the estimate of the beam equation can be used not only for clearance measurement but also for periodic monitoringof the beam shape over time.
2 Theoretical backgrounds
2.1 Photogrammetric process
Close range photogrammetry is a non-destructive geomatic technique which allows the 3D shape of objects to be reconstructed from photographic images. The conversion from 2D information of images to 3D models is achieved by means of the photogrammetric process. Two main steps contribute to this process: inner orientation and external orientation. The inner orientation reconstructs the internal geometry of the imaging system, which defines the perspective system, by means of the camera calibration process. The metric parameters obtained from the camera calibration include the 3D position of the perspective centre in the image space (focal length and principal point on the sensor), sensor dimensions, and lens distortions. The lens distortions are sources of errors during the image recording and must be compensated for to obtain the most accurate reconstruction of the 3D model. The symmetric radial distortion significantly influences the photogrammetric reconstruction as shown in [28,29]. There are two common formulations for radial distortion: balanced and unbalanced models. Although these models can be mathematically equivalent, the balanced model results in smaller apparent distortions so is commonly used by camera and lens manufacturers [30–32]. The external orientation locates the relative position of each camera used in the 3D reconstruction process at the time images were taken. Hence, if the position of one camera is known, the relative external orientation is done using the positions (X, Y, Z) and orientations (ω, φ, κ) of the other cameras. For a given point in an object space, the coplanarity condition requires that the point's position in two overlapped images and the camera's perspective centre are situated in the same plane. As shown by Krauss in [33], the relative orientation of images is achieved when the image coordinates of Fig. 1.
Fig. 1. Measurement of minimum vertical underclearance during a routine bridge inspection
Measurement of minimum vertical underclearance during a routine bridge .Inspection five points are known. The external orientation is completed when the model is scaled and placed in the absolute coordinate system.When the relative camera position is solved, the camera perspective centre Oi, a point in the image (xi, yi), and the position of this point over the surface of the object (X, Y, Z) are located in the same straight linebased on the collinearity equation. It is then possible to obtain the 3D position of a point on the object surface from measurements in the image. The mathematical principles of this process are further explained in [34] and [35].
2.2 3D fitting algorithm
The shape of object surfaces can be usually modelled by means of parametric surfaces. When a set of data points defining the object surface is available, a function of two independent variables (x and y) can be determined to best fit a parametric surface to the data. For 3D curve fitting, a dependent variable f can be modelled from two independent variables x and y, where data are a set of n3D points (xi, yi, fi), for i=1: n, n∈N. In this case, object points with three spatial coordinates (xi, yi, zi) are obtained from the photogrammetric process. Xi and Yi components of space points are initially aligned according to transversal and longitudinal bridge's directions, respectively. Zi corresponds to the vertical component (clearance direction).This 3D information provides the two independent variables (x and y) as well as a third component zi for the minimization of the following expression.
3 Methodology
3.1 Instrumentation
To be feasible, an important aspect to consider in the effort to enhance routine bridge inspection work is maintaining the simplicity of equipments used for basic inspection tasks while providing better documentation. For this reason, the measurement procedure developed in this study was based on simple field setups and the usage of digital cameras which do not require advanced knowledge of digital image recording by operators. A digital, semi-metric camera (Canon EOS 10D) equipped with a CCD sensor, RGM matrix resolution of 6.29 million pixels and a Canon EF 20 mm f/2,8 lens was used for image acquisition. External information with real dimensions of a reference body is required in order to get the 3D model scaled. In this sense, duringthe execution of this project a reference distance was obtained by means of measuring coordinates of two control points. To validate the photogrammetric results, separate measurements using topographic equipment were made. A total station (Leica model TCR 1203+) was used to measure a set of points defining the lower profile of the beam and control points. The technical features of the instrument include long-range coverage (up to 400 m); ±2 mm+2 ppm accuracy; 10 cc angular accuracy (1 cc typical average measurement in angles deviation);and 6″/2 mm sensitivity of levels.
3.2 Camera calibration
The cameras are calibrated under fixed imaging parameters in the laboratory prior to the field work. Consequently, operators only have to acquire a few photographs during the actual bridge survey (field calibration requires significantly more photographs). The camera calibration process is performed in the “Calibration module” of the Photomodeler Pro? software using a scaled planar grid of points which is captured by means of several images from different points of view. The calibration images are marked and imported into the photogrammetric platform where the geometric parameters of the camera are almost automatically obtained. The parameters representing the inner orientation of the camera used in this study are presented in Table 1, as well as the components of the mathematical polynomials that model the radial (K1 and K2) and tangential (P1 and P2) lens distortions. Based on the sensor dimensions given in the table, the pixel size amounts to 7.3 μm, which together with the principal distance of the image system, determines the maximum perceived detail of objects captured in a digital image. The spatial resolution of an image over the object surface can be calculated as the pixel size projection or GSD (ground sample distance) by means of the following expression(2),where, A is the mean distance to the object, f is the principal distance of the calibrated camera and sx is the pixel size calculated from the CCD size of the camera sensor and image resolution. Based on the computed values of pixel size and principal distance, for instance, the pixel size projection expected is 11 mm if an operator is working with averaged object distances of 30 m. Consequently, the minimum error of measurement from images will exceed this value.
3.3 Data acquisition
Once the cameras are calibrated, they can be directly used in the field. For the measurement of vertical clearance, as well as other geometric features, the methodology for data acquisition consists of the following steps:
? Selection of camera parameters according to the internal configuration determined from camera calibration.
? Definition of camera stations. According to the princ
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