Rapid Beam Replacement of Chongqing Monorail: Emergency Beam, Process, and Technologies

Zhang Cai-ran, Zhu Er-yu, Cheng Jing-fu School of Civil Engineering and Architecture, Beijing Jiaotong University

Beijing Jiaotong University, BJTU Beijing, China

e-mail address: zcr0705@163.com

Abstract—Chongqing monorail line 2 ， the first straddle monorail transit in China, was opened to public in 2005. Most of the track beams in the monorail system are prestressed concrete (PC) beams. Because of its complicated alignment and long construction time, once a PC beam is destroyed, the whole line will be out of operation for a long time. To respond to the potential threats on PC beam, a research project was conducted to solve the problem of rapid beam replacement. To achieve the research objectives, the research team first introduced a new type of prefabricated emergency beam, which can be temporarily used to shorten the idling time of the monorail system. Then the research team developed the process of rapid beam replacement for PC beam accident. Next, two key technologies, emergency beam assembling and installation, were studied so that the rescue works would be carried out successfully. This research work could ultimately enhance the capability of rapid beam replacement after extreme events.

Keywords-emergency beam; rapid beam replacement; assembling; installation; emergency supports; straddle monorail

I. INTRODUCTION China’s first monorail system officially opened on June 18,

2005 in Chongqing, as shown in Fig.1. The system is 19km long and has 18 stations. The line starts at Jiaochangkou in the city’s central district and ends in the industrial area of Xinshancun. Under construction since January of 2001, the initial line includes 2.5km subway tunnel. Then it was extended to Fengshouba. The whole line was opened on July 1, 2006. Chongqing Monorail is capable of carrying 30,000 passengers per hour at peak hours. In this system, most of the track beams are PC beams. The construction time of a PC beam is 104 days. The alignments of PC beams are various and complicated, once a PC beam is destroyed, the whole line will be out of operation for a long time.

Researches on rush bridge repair have been widely studied. By studying three cases of previous bridge replacements following extreme events, Bai, Yong determined the processes and techniques that were used in the rapid bridge replacements and outlined needed improvements [1]. Unsworth, John F described the planning and techniques used in the rapid replacement of a movable steel railway bridge with minimal interruption to railway and marine traffic [2]. Landers, Jay described emergency repairs to various bridges damaged by

Hurricane Katrina in Louisiana and Mississippi [3]. Scanlon, Andrew designed a prefabricated bridge system to minimize on-site construction time. The system consists of a double-cell adjacent box beam superstructure supported on precast post-tensioned abutment units on cast-in-place footings [4]. Saiidi, M. Saiid developed a method to utilize fiber composites for rapid repair of earthquake damaged flared columns [5]. Yang Xingming investigated the rush repair of railway bridges in high-tech war [6]. Liu Jiawu proposed a “two accelerations” viewpoint, which means that not only the assembling and installation speed of steel girders for rush repairs, but also the running speed of the train should be accelerated [7]. Zhang, Cairan divided the damaged PC beams of Chongqing monorail into five levels and proposed that the beam must be replaced when it is at the fifth level [8]. However, there is little research on rapid beam replacement of straddle monorail.

In this paper, we focus on the replacement of destroyed PC beam by emergency (temporary) beam. First, the structure of emergency beam will be introduced in section Ⅱ. Second, the rapid beam replacement process will be presented in section Ⅲ. Third, two key techniques for rapid beam replacement, emergency beam assembling and installation, will be outlined in section Ⅳ. Finally, the writers will present conclusions in section Ⅴ. The research results will ensure the PC beams of straddle monorail replaced rapidly after extreme events.

Figure 1. Chongqing monorail

National Natural Science Foundation of China (50778022)

978-1-4244-4639-1/09/$25.00 ©2009 IEEE

II. EMERGENCY BEAMS Using temporary bridges will be the fastest and best way to

accommodate traffic while the permanent bridge is under reconstruction. All the components of our emergency beam were divided into 3 types (standard sections, bearing sections, adjust sections), 4 curve radius(R=117m, 177m, 363m, ∞m). The section library of emergency beams for one curve radius is shown in Tab.1. Selecting needed sections, we can assemble an emergency beam and its length error is less than 0.005m comparing with the destroyed PC beam. The standard section height of the emergency beam is 2.3m, as shown in Fig.2. The bearing section with variable heights (1.6m~1.8m~2.3m), as shown in Fig.3. The adjust section height is 1.6m.

When a PC beam damaged and needs to be replaced, we can assemble an emergency beam (Fig.4) by the selected sections. The sections are connected by connecting plates and high-strength bolts.

Figure 2. Standard section

III. PROCESS OF RAPID BEAM REPLACEMENT Beam replacement is a complicated operation that involves

many parties. It requires each party to make technical and management decisions at different stages in a very short period of time. A general model was developed to represent the process, as shown in Fig.5. This model includes three subjects: destroyed PC beam demolition, emergency beam installation and demolition, and new PC beam installation. Once we incept alarm, destroyed PC beam demolition, emergency beam assembling and new PC beam construction began simultaneously. After the emergency beam assembling is completed and the destroyed PC beam demolition is finished, then emergency beam is transported to construction site immediately, and the emergency beam installation began. The emergency beam will be operating until the new PC beam is accomplished. When the new PC beam put into operation, the emergency rescue is over.

Figure 3. Bearing section

TABLE I. SECTION LIBRARY OF EMERGENCY BEAM

Section number

Section type Quantity Description Total length

1 standard section 5 (parts) 2×7(m), 4(m), 2(m), 1(m) 21(m)

2 bearing section 7 (parts) 2×2.0(m), 2.1(m), 2.2(m), 2.3(m), 2.4(m), 2.5(m) 15.5(m)

3 adjust section 10 (parts) 0.10(m), 0.11(m), 0.12(m), 0.13(m), 0.14(m), 0.15(m), 0.16(m), 0.17(m), 0.18(m), 0.19(m) 1.45(m)

Figure 4. Assembled emergency beam

Figure 5. Process of rapid beam replacement

The emergency beam, as an alternative of the destroyed PC beam, maintains the traffic when the new PC beam is being constructed. The construction time of a PC beam, as long as 104 days, has little influence on the traffic. The time delays and traffic disruption due to the destroyed PC beam are minimized.

IV. KEY TECHNOLOGIES The emergency beam for Chongqing monorail is assembled

by prefabricated steel sections, and the time of emergency beam assembling and installation is the most important to the whole process. So, emergency beam assembling and installation are two key technologies in the emergency rescue.

A. Emergency beam assembling Fig.6 shows the emergency beam assembling process, and

it must be rapid and accurate. Thus, we developed software to guide the emergency beam assembling, as shown in Fig.7. After input the serial number of the destroyed PC beam, the section list and assembling guidebook of its corresponding emergency beam will be output in a few minutes.

Using this software, we can easily get the needed sections for any PC track beam. For example, if a PC beam is destroyed, we input its serial number (Z213-06), and then the information of the corresponding emergency beam will be output (Fig.7). The emergency beam’s radius is 363m, and it should be assembled by three standard sections (one is 1m long and the others are 7m long), two bearing sections (one is 2.4m long and the other is 2.5m long) and one adjust section (140mm long). The error of arrow height, intersection angle and length are also given. Then we click the “Construction book” button and the assembling manual book will be output in AutoCAD.

Figure 6. Emergency beam assembling process

Figure 7. Interface of software for emergency beam assembling

Tools preparingRun software

Assembling

Acceptance inspection

PC beam destroyed

Sections preparingOutput the section

library

Destroyed PC beam demolition

Emergency beam assembling and installation

PC beam destroyed

New PC beam construction

New PC beam operation

Emergency beam operation

Emergency beam demolition

Emergency beam installation and demolition

Destroyed PC beam demolition

New PC beam installation

New PC beam installation

B. Emergency beam installation The altitude of Chongqing Monorail traffic regional is l80m

~ 430m. Monorail system climbing capacity is 60‰ ~ 80‰, slope length up to 400m above. Line crosses three main densely populated regions, surrounded by many large commercial office facilities, parks, hospitals, schools and other facilities. The installation schemes of emergency beams must adapt to the site situations, and we classify them by choosing different erection equipments as following.

1) Mobile crane Range of application: the road is wide enough for the trailer

and mobile crane access freely, and its bearing capacity satisfies the emergency beam transportation and erection. There are no barriers in the operating range of mobile cranes.

Construction procedure: assembling the emergency beam in production factory firstly, and then it is transported to the construction site by trailer. Next, using two mobile cranes erect the emergency beam.

2) Simple creeper crane Range of application: at the bridge site where the work

space is enough and traffic is convenient, we can use simple creeper crane, which is assembled by facilities, to erect emergency beam.

Construction procedure: transporting the assembled emergency beam to the construction site, and then using simple creeper crane erect the emergency beam.

3) Special creeper crane Range of application: in the gorge areas or tunnels where

the mobile crane could not access, and there is no enough work space for simple creeper crane assembling.

Construction procedure: the emergency beam is assembled in production factory and then it is transported to the construction site. Finally, using special creeper crane erect the emergency beam.

No matter which installation scheme is chosen, the safety of constructors, pedestrian and equipments etc. is the chief problem. In addition, the installation work should minimal the traffic disruption, erection time and cost.

V. CONCLUSIONS Because constructing for a new PC beam needs 104 days,

once a PC beam is destroyed, the whole line will fail for a long time. In order to improve the ability that monorail transportation enterprises cope with track beam accident, and dispose PC track beam accident rapidly and effectively, rapid replacement for destroyed PC beam of Chongqing monorail was studied in this paper. The following conclusions are drawn from this research project.

(1) The design of emergency beam, using the installation scheme of prefabricated sections, not only makes rapid beam assembling possible, but also ensures that the sections can be used repeatedly. Bearing section with variable heights can be securely connected with standard section and bearing.

(2) The process of rapid beam replacement includes three subjects: demolition of destroyed PC beam, emergency beam installation and demolition, and new PC beam installation. Three subjects carried out simultaneously and coordinate each other that enable the monorail system come back to operation soon. This process both releases traffic pressure and reduces economic loss.

(3) Emergency beam assembling and installation are important links in emergency beam construction. The software for emergency beam assembling can output the assembling guidebook easily, and the installation schemes were classified by site situations. They make the rapid rescue possible.

ACKNOWLEDGMENT The writers would like to thank all individuals who made

this research possible. A special thanks to Chongqing Monorail Transport Company who provided guidelines and financial support for this research project.

REFERENCES [1] Bai, Y., and Burkett, W. R.，“Rapid Bridge Replacement: Processes,

Techniques, and Needs for Improvements,”. J. Constr. Eng. Manage.vol.132, No.11,pp.1139-1147, November 2006.

[2] Unsworth, John F., and Brown, Christian, “Rapid replacement of a movable steel railway bridge,” Transportation Research Record. No.1976, pp. 31-35, 2006.

[3] Landers, Jay, “Structural engineering: Louisiana, Mississippi rush to repair highways damaged by Hurricane Katrina,”. Civil Engineering. vol. 75, No. 11, pp. 13-14, November 2005.

[4] Scanlon, Andrew., Aswad, Alex., and Stellar, James, “Precast posttensioned abutment system and precast superstructure for rapid on-site construction,”. Transportation Research Record. No. 1814, pp.65-71, 2002.

[5] Saiidi, M. Saiid., and Cheng, Zhiyuan, “Effectiveness of composites in earthquake damage repair of reinforced concrete flared columns,” J. Compos. for Constr. vol. 8, No. 4, pp. 306-314, July/August 2004.

[6] Yang Xingming, “Research into the Rush Repairs of Railway Bridges in Hi-Tech War,”Traffic Engineering and Technology for National Defence.Chinese, No.3, pp. 5-6, 2005.

[7] Liu Jiawu, “The Study of Rush Repair of Railway Bridges During the New Period Should Have Its Greater Stress Placed on the ‘Two Accelerations’, ” Traffic Engineering and Technology for National Defence. Chinese, No.4, pp. 1-4, 2006.

[8] Zhang. CR., and Zhu. EY, “Research on evaluation methods and reinforcement measures of PC track beams used in monorail traffic,” 2nd International Conference on Structural Condition Assessment, Monitoring and Improvement (SCAMI-2)., Changsha, 2007, Vols 1 And 2, pp. 607-611.