CONSIDERATIONS FOR DEVELOPMENT OF HIGH SPEED RAIL BRIDGE DESIGN STANDARDS
Y. Edward Zhou URS Corporation 4 North Park Drive Hunt Valley, Maryland 21030 Telephone: 301-820-3539 Fax: 301-820-3009 Email:
[email protected] Suoting Hu China Academy of Railway Sciences No. 2 Daliushu Road, Haidian District Beijing, China 100081 Email:
[email protected] Zaitian Ke China Academy of Railway Sciences
ABSTRACT
Compared with conventional railways, high speed rail (HSR) has stricter requirements on bridge structural stiffness to minimize deformations and avoid excessive vibrations or resonance due to train crossings at high speeds. Bridge design for HSR requires a good understanding of traintrack-structure dynamic interactions, requirements for deflections, rotations, and natural frequencies of bridge spans, as well as continuous welded rail (CWR)-structure interactions. A review of China’s recent developments in HSR can benefit the development of HSR bridge design standards in North America. In China, commercial operation of passenger trains up to 250 km/h (155 mph) began in 2007 on existing rail lines that serve mixed passenger and freight trains. After 2007, construction of commercial passenger dedicated lines (PDL’s) started since further upgrading of mixed-traffic rail lines for higher speeds was considered unpractical and uneconomical. China released its Code for Design of High Speed Railway in late 2009 for passenger train design speed between 250 km/h (155 mph) and 350 km/h (217 mph). The
ABSTRACT
Compared with conventional railways, high speed rail (HSR) has stricter requirements on bridge structural stiffness to minimize deformations and avoid excessive vibrations or resonance due to train crossings at high speeds. Bridge design for HSR requires a good understanding of traintrack-structure dynamic interactions, requirements for deflections, rotations, and natural frequencies of bridge spans, as well as continuous welded rail (CWR)-structure interactions. A review of China’s recent developments in HSR can benefit the development of HSR bridge design standards in North America. In China, commercial operation of passenger trains up to 250 km/h (155 mph) began in 2007 on existing rail lines that serve mixed passenger and freight trains. After 2007, construction of commercial passenger dedicated lines (PDL’s) started since further upgrading of mixed-traffic rail lines for higher speeds was considered unpractical and uneconomical. China released its Code for Design of High Speed Railway in late 2009 for passenger train design speed between 250 km/h (155 mph) and 350 km/h (217 mph). The
INTRODUCTION
UIC (International Union of Railways) defines high speed rail (HSR) as systems of infrastructure and rolling stock which operate at speeds of 250 km/h (155 mph) or higher on specially built new lines, or the order of 200 km/h (124 mph) on specially upgraded existing lines (1). It is commonly recognized that the first modern commercial HSR was Japan’s Shinkansen between Tokyo and Osaka, which started operation in 1964 with a top speed of 256 km/h (159 mph). In Europe, regular HSR services started in the 1970’s in France, Italy, Germany, Spain, and the Great Britain. China began research and planning on high speed rail (HSR) feasibility and technologies in early 1990’s. A long debate was held over the type of technology to be employed for large scale application: conventional rail vs. magnetic levitation (maglev). Finally in 2006, the government decided to adopt the conventional wheel-rail technology for China’s HSR network. Nevertheless the 30 km (18.6 mi) long Shanghai Maglev Demonstration Operation Line began
dedicated lines (PDL’s) started after 2007 since further upgrading of mixed-traffic rail lines for higher speeds was considered unpractical and uneconomical. China's HSR network consists of upgraded conventional rail lines and newly-constructed PDL’s. As of June 2011, China has the world's largest in-service HSR network totaling approximately 9,700 km (6,027 miles), including approximately 3,500 km (2,175 miles) with top speed of 300 km/h (186 mph) or 350 km/h (217 mph). The best-known section of PDL is the Beijing-Shanghai High Speed Railway that opened to the public in June 2011 with a design top speed of 380 km/h (236 mph). mph). The Chinese made CRH380 train-sets operate on this line. Bridges account for approximately half of the total length on China’s PDL’s. Prior to opening a line for service, the bridges are usually tested with a special train at a range of speeds up to 110% of the design speed. The primary purpose of the test is to verify the traction and power system and collect wheel-rail interaction data. Acceleration data is often collected from these tests for characterizing the fundamental dynamic behavior of bridges.
In addition, HSR lines require smoother geometrical alignment for horizontal curves and vertical profiles to ensure safe and comfortable operation of trains traveling at high speeds.
HSR BRIDGE DESIGN CODES
UIC Code Leaflet 776-2 Design requirements for rail-bridges based on interaction phenomena between train, track and bridge (2) provides HSR bridge design requirements specifically for
serviceability limit states concerning deformation and vibration. The UIC Code has other leaflets that contain provisions for HSR bridge design, including Leaflet 776-1 Loads to be considered in railway bridge design (3) and Leaflet 774-3 Track/bridge Interaction Recommendations for calculations (4). European standards BS EN 1990:2002 Eurocode – Basis of Structural Design
(5) establishes principles and requirements for structural design and is intended to be used in conjunction with EN 1991 to EN 1999 for the design of various types of civil structures. For example, BS EN 1991-2:2003 Eurocode 1: Actions on structures – Part 2: Traffic loads on
HSR TRACK ALIGNMENT REQUIREMENTS
For track horizontal curves, the Chinese HSR code provides radius requirements for different design speeds in the form of: “recommended radius”, “minimum radius – general”, “minimum radius – special” (requiring technical and economical comparison as well as approval by the Ministry of Railway), and “maximum radius”. Table 1 lists the Chinese HSR horizontal curve radius requirements for main lines for different design speeds in Metric and US Customary units. Also provided in the table are the degrees of curve corresponding to the radius requirements. The Chinese HSR Code also has detailed requirements for horizontal transition spirals.
TABLE 1. Main Line Horizontal Curve Radius and Degree Requirements from Chinese HSR Design Code. Track Type \ Design Speed
Radius (m)
350/250 km/h (217/155 mph) 8,000 - 10,000 m
300/200 km/h (186/124 mph) 6,000 - 8,000 m
250/200 km/h (155/124 mph) 4,500 - 7,000 m
250/160 km/h (155/99 mph) 4,500 - 7,000 m
For main line track vertical profiles, the Chinese HSR code specifies a maximum gradient of 20‰ (2%) in normal condition and 30‰ (3%) in difficult condition pending technical and economical comparisons. In sections that are for trainsets made of motorized cars, the maximum allowed gradient is 35‰ (3.5%). The Chinese HSR Code also has detailed requirements for gradient changes and vertical curves.
OVERVIEW OF CHINA’S HSR BRIDGE DESIGN STANDARDS
The Chinese HSR bridge design specifications are similar to UIC’s with adjustments made for specific situations in China based on results of analytical and field experimental research conducted in the past two decades. In the Chinese Code for Design of High Speed Railway ( 7 ), Chapter 7 Bridges and Culverts consists of the following sections: 7.1 General provisions 7.2 Design loads
TABLE 2. Design Loads for Bridges and Culverts. Loading Types
Permanent
Loading Description Selfweight of strutural components and auxiliary facilities Prestressing forces Effects of concrete shrinkage and creep Earth pressure Static water pressure and buoyancy Effects of foundation movements
Vertical train static live loads Vertical highway static live loads (as applicable) Vertical dynamic impact of train loads Longitudinal and flexural interaction forces with CWR Transient Centrifugal forces Lateral oscillation force s Train live load induced earth pres sure Pedestrian and railing loads Aerodynamic loads Train tracti on and braking forces Wind loads Flow pressure Secondary loads Ice pressure Effects of temperature changes Freezing expansio
Primary loads
FIGURE 1. China HSR ZK Standard Live Load.
FIGURE 2. China HSR ZK Special Live Load.
continuous superstructures of three or more spans, the limits in Table 3 are to be multiplied by a factor of 1.1. For continuous or simply spans of two or less, the limits in Table 3 are to be factored by 1.4. For single-track simple or continuous spans, the limits in Table 3 are to be factored by 0.6.
TABLE 3. Vertical Deflection Limits for Double-Track Simple-Span Concrete Girders of Span Lengths less than 96 m (315 ft). Design Speed km/h (mph) 250 (155) 300 (186) 350 (217)
L ≤ 40 (131) L/1,400 L/1,500 L/1,600
Span Length Range, m (ft) 40 (131) < L ≤ 80 (262) L/1,400 L/1,600 L/1,900
L > 80 (262) L/1,000 L/1,100 L/1,500
For arch and rigid frame bridges, structural deflections must also take into consideration of temperature effects, in addition to live load actions. For prestressed concrete bridges, creep
For girder ends at piers, the rotation (θ1 or θ2) of each girder end needs to satisfy the limit for the girder end at abutment (θ) in addition to the requirements for the sum of girder end rotations in adjacent spans (θ1 + θ2).
TABLE 4. Limits for Vertical Girder End Rotations. Track Type Ballasted
Location between abutment and span between adjacent s pans between abutment and span
Ballastless between adjacent spans
Limit (rad) θ ≤ 2.0‰ θ1 + θ2 ≤ 4.0‰
Girder End Cantilever, Lc, m (ft)
θ ≤ 1.5‰
Lc ≤ 0.55 m (1.80 ft) 0.55 (1.80) < Lc ≤ 0.75 (2.46) Lc ≤ 0.55 m (1.80 ft) 0.55 (1.80) < Lc ≤ 0.75 (2.46)
θ ≤ 1.0‰ θ1 + θ2 ≤ 3.0‰ θ1 + θ2 ≤ 2.0‰
Requirements for Vertical Natural Frequencies of Girders
Requirements for dynamic characteristics of bridge spans are established based upon criteria in consideration of dynamic responses of the structure, safety of crossing trains, as well as ride
TABLE 5. Vertical Vibration Natural Frequency Lower Limits for Double-Track Simple-Span Concrete Box Girders of Common Lengths Not Requiring Dynamic Analysis. Span Length m (ft) 12 (39) 16 (52) 20 (66) 24 (79) 32 (105)
Design Speed, km/h (mph) 250 (155) 300 (186) 100/L 100/L 100/L 100/L 100/L 120/L
100/L 100/L 120/L 130/L
350 (217) 120/L 120/L 120/L 140/L 150/L
For bridges that are beyond the coverage of Table 5, dynamic analysis for train-structure coupling vibrational responses is required based on the actual condition of train crossing and a maximum train speed of 1.2 times the design speed. The following requirements must be satisfied : Wheel-climb derailment factor:
Q/P ≤ 0.8
where, Q = lateral wheel load on rail, kN (1 kN = 225 lbs force); P = vertical axle load, kN; P0 = static axle weight, kN; ∆P = reduction of vertical axle load due to dynamic action; g = standard gravity = 9.81 m/s2 (32.174 ft/s2 ).
Requirements for Longitudinal Stiffness of Piers and Abutments
For simple-span concrete girders located in the fixed zone (no longitudinal rail movements due to temperature) of ballasted continuous-welded-rail (CWR) track, longitudinal stiffness at the top of piers and abutments must be no lower than the limits listed in Table 6 (7 ).
TABLE 6. Longitudinal Stiffness Limits for Top of Piers and Abutments. Type
Span m (ft) ≤ 12 (39) 16 (52) 20 (66)
Min. Longitudinal Stiffnes s, kN/cm (kip/in) Double-Track Single-Track 100 (57) 60 (34) 160 (91) 190 (108)
100 (57) 120 (69)
Girder Vibration Frequency Requirements
Crossing trains act as vibration excitation sources to bridge girders. The excitation frequency varies with train speed. As the excitation frequency approaches the natural frequencies of the structure excessive vibrations or even resonance may occur. These dynamic responses can cause damages to the track system and the structure, or even threaten the safety of the crossing train or the bridge. Factors affecting train-bridge dynamic responses include natural frequencies of the girder, damping ratio of the structural system, train speed, car length and truck spacing, track irregularities, flat wheels, etc. Previous research suggested that the primary factors affecting the vertical excitation frequency of train loading are the train speed and car length. The effects of other factors such as the axle spacing and truck spacing are secondary because their repeated actions are not continuous. Thus the excitation frequency is simply:
(a) 32 m (105 ft) Box Girders
(b) 24 m (79 ft) Box Girders
FIGURE 4. Field Measured Correlation between Vertical Excitation Frequency and Train Speed.
UIC’s requirements for bridge girder natural frequencies consist of the upper bound and lower bound for varying span lengths. The lower bound is to control excessive vibration or resonance due to train crossings; and the upper bound is to limit train-track dynamic responses due to track irregularities. For bridge girders of natural frequencies within the required envelope
high magnitudes of these lower limits for actual girders and the low magnitudes of track irregularities permitted by inspection requirements. Figure 5 shows comparisons between computed and field measured dynamic impact for 32 m (105 ft) simple-span concrete box girders due to the CRH2 train sets (8 ). The figure clearly demonstrates that girders not satisfying the natural frequency requirements in Table 5 (≥130/L at 300 km/h, ≥150/L at 350 km/h) can be subject to excessive dynamic response or resonance at train speeds higher than 300 km/h (186 mph).
Computed (natural freq. = 150/L) ) µ + 1 ( t c a p m I c i m a n y D
Computed (natural freq. = 120/L) Field Measured (loaded trains) Field Measured (empty trains)
ft/s2), for varying train speed. However, different countries use different live loads for the calculation of maximum girder deflection (δ) for double-track bridges. For example, UIC uses single-track design live load with dynamic impact; Japan uses single-track operating live load including dynamic impact; China uses the standard ZK design live load on both tracks but not including dynamic impact. Comprehensive comparative studies were made in China for varying span lengths considering factors such as single-track vs. two-track loading, variation of design live load among different countries, tolerances for track irregularities, etc. Figure 6 depicts computer models used for calculating static and dynamic responses of concrete box girders to crossing train loads. Such research yielded Table 3 as the result.
girder end rotation imposes push-down and uplift forces, respectively, to the rail on either side of the gap between the girder ends. These forces may cause damages to the ballast, rail fasteners, or the slab system if not controlled properly. Research in China suggested limits for vertical girder end rotations (9), as summarized in Table 4, for ensuring proper performance of the rail-fastenerslab system, reducing maintenance needs, and ensuring the safety of crossing trains at high speeds.
Fastener 扣件 Rail 钢轨 梁 Girder
Girder 梁
FIGURE 7. Illustration of Bridge Girder End Rotation and Impact to Rail-Fastener-Slab System.
etc. (10). The results from such research have provided great value and detailed provisions to proper design of bridges and track systems for HSR. Distribution of train braking forces among bridge substructure depends on the longitudinal stiffness of adjacent bridge piers and abutments. Research in China suggested that the longitudinal stiffness of bridge substructure is an important design parameter; and Table 6 was developed as a result to provide longitudinal stiffness limits for the top of piers and abutments in the fixed zone of ballasted CWR. Since the braking force only considers one train for double-track bridges in the Chinese bridge design standards, values in Table 6 are to be multiplied by a factor of 2.0 for piers and abutments supporting elevated train stations within the departing and approaching limits to consider the simultaneous occurrence of traction and braking forces on both tracks.
CONCLUSIONS
km/h (217 mph). Much of their research results and bridge design standards can be used as a good resource for the development of HSR bridge design standards in North America.
REFERENCES
(1)
UIC
(International
Union
of
Railways),
General
definitions
of
highspeed
http://www.uic.org/spip.php?article971, retrieved June 2012 (2)
UIC (International Union of Railways), Leaflet 776-2, Design requirements for railnd
bridges based on interaction phenomena between train, track and bridge , 2 edition, June
2009 (3)
UIC (International Union of Railways), Leaflet 776-1 Loads to be considered in railway th bridge design , 5 edition, August 2006
(4)
UIC (International Union of Railways), Leaflet 774-3 Track/bridge nd
Recommendations for calculations , 2 edition, October 2001
Interaction
Proceedings of 60th Anniversary Symposium of China Academy of Railway Sciences, China Railway Press, Beijing, 2010 (9)
Niu, B., Hu, S., Wei, F., Ma, L., Research and Applications of Prestressed Concrete Box th
Girders in China’s High Speed Railway (in Chinese), Proceedings of 19 China Bridge Engineering Conference, Shanghai, 2010 (10) Lu, Y., Research and Application of Continuous Welded Rail Track (in Chinese), China Railway Press, 2004
LIST OF TABLES TABLE 1. Main Line Horizontal Curve Radius and De gree Requirements from Chinese HSR Design Code. TABLE 2. Design Loads for Bridges and Culverts. TABLE 3. Vertical Deflection Limits for Double-Track Simple-Span Concrete Girders of Span
FIGURE 5. Comparison between Computed and Field Measured Dynamic Impact for 32 m (105 ft) Simple-Span Concrete Box Girders. FIGURE 6. Computer Models for Dynamic Responses of Concrete Box Girders. FIGURE 7. Illustration of Bridge Girder End Rotation and Impact to Rail-Fastener-Slab System.
2012 Annual Conference & Exposition
Considerations for Development of High Speed Rail (HSR) Bridge Design Standards Ed Zhou (1), Suoting Hu (2), Bin Niu (2), & Zaitian Ke (2) (1) URS
Corporation (2) China Academy of Railway Sciences (CARS)
September 16-19, 2012 ! Chicago, IL
2012 Annual Conference & Exposition
HSR – Definition & Major Milestones • UIC (International Union of Railways)’s HSR definition: systems of infrastructure and rolling stock which operate at speeds of – 155 mph (250 km/h) or higher on specially built new lines, or – the order of 124 mph (200 km/h) on specially upgraded existing lines
• First modern commercial HSR: Japan’s Shinkansen between Tokyo and Osaka, which started operation in 1964 with a top speed of 159 mph (256 km/h ). • In Europe, regular HSR services started in the 1970’s in France, Italy, Germany, Spain, and the Great Britain. September 16-19, 2012 ! Chicago, IL
2012 Annual Conference & Exposition
HSR Bridge Design Codes • UIC Code – BS EN 1990:2002 Eurocode – Basis of Structural Design – BS EN 1991-2:2003 Eurocode 1: Actions on structures – Part 2: Traffic loads on bridges – Leaflet 776-1 Loads to be considered in railway bridge design – Leaflet 776-2 Design requirements for rail-bridges based on interaction phenomena between train, track and bridge – Leaflet 774-3 Track/bridge Interaction Recommendations for calculations
• Chinese Code • Other… September 16-19, 2012 ! Chicago, IL
2012 Annual Conference & Exposition
China’s HSR Network for 11th 5-Year Plan (2006 ~ 2010)
September 16-19, 2012 ! Chicago, IL
2012 Annual Conference & Exposition
HSR Development History in China • Early 1990’s: began research on feasibility and technologies. • 1998 ~ 2006: debate on national HSR technology, finally decided to adopt the conventional wheel-rail track over maglev (magnetic levitation). • 1999 ~ 2003: constructed a 251 mi. (404 km ) passenger dedicated line (Qin-Shen) of design and operating speed of 124 ~ 155 mph (200 ~ 250 km/h), with top test speed of 186 mph (300 km/h), serving as the national research/testing/practice base for HSR technologies. • 2000 ~ 2004: constructed world’s first commercial HS maglev in Shanghai, 19.0 mi. (30.5 km) long, 267 mph (431 km/h) top speed, of German technology. September 16-19, 2012 ! Chicago, IL
2012 Annual Conference & Exposition
HSR Development History in China (cont’d) • 1997 ~ 2007: conducted six rounds of “speed-lift” campaigns on existing lines across the country, increasing passenger train speed up to 124 – 155 mph (200 – 250 km/h) on multiple existing rail lines that served mixed passenger and freight trains. • 2007 ~ : started developing commercial passenger dedicated lines (PDL), because further upgrading of mixed-traffic rail lines for higher speeds (> 155 mph, or 250 km/h) was considered unpractical and uneconomical. • By June 2011 (after opening of Beijing–Shanghai HSR line), in-service HSR mileage totaled ±6,027 miles (9,700 km), including ± 2,175 miles (3,500 km) of 186 ~ 217 mph (300 ~ 350 km/h) top speed. September 16-19, 2012 ! Chicago, IL
2012 Annual Conference & Exposition
Development Process of China’s HSR: Four Stages "# $%&'()*)+, -&&./.*01)( 2# 3/4)51(+ 6 78+%91)( :# -;9)5;8(+ 6 3/45)# 3(()-&J1>0' 23'7+&$& L*+.&+1 *' ,*9&. P3'& 3A K0--01$&. 2QR Type
Pier
Abutment
Span m (ft) ! 12 (39)
Min. Longitudinal Stiffness, kN/cm (kip/in) Double-Track Single-Track 100 (57) 60 (34)
16 (52) 20 (66) 24 (79) 32 (105)
160 (91) 190 (108) 270 (154) 350 (200)
100 (57) 120 (69) 170 (97) 220 (126)
40 (131) 48 (157)
550 (314) 720 (411) 3,000 (1,713)
340 (194) 450 (257) 1,500 (857)
• For areas within departing and approaching limits of elevated stations, the stiffness limits are multiplied by a factor of 2.0 September 16-19, 2012 ! Chicago, IL
2012 Annual Conference & Exposition
China – U.S. Similarities in HSR Development • Large territory and immense railway track mileage • Develop HSR via a transition process from existing railway tracks that serve mixed passenger and freight trains. • China is the only country that runs commercial train service on conventional rail lines up to 217 mph (350 km/h ). • Much of their research results and bridge design standards can be utilized as a good resource by AREMA.
September 16-19, 2012 ! Chicago, IL
