Defense thesis

Precast Pre-stressed Concrete Girder Bridge

Dissertation Presented in Partial fulfillment for the Bachelor of Science in Department of Civil Engineering Jiangsu University

Dissertation Defense by Nkosiyabo Isaac Mafu

Dissertation Committee

Assoc. Prof: Dr.Jie Yin Assoc. Prof: Dr. Bo Su Assoc. Prof: Dr. Hai-Xia XU Lecturer Dr. Hai QIAN (Secretary)

Contents• Overview of the bridge• Objectives• Design steps• Superstructure design• Bridge layout• Beams• Shear reinforcement • Substructure and foundation

Overview of the bridge• This project Site location is assumed to be near Socorro, New Mexico, with

the bridge crossing a waterway on a normal (perpendicular) alignment.• We illustrates New Mexico Department of Transportation (NMDOT) design

procedures for a three-span pre-stressed concrete girder bridge. The bridge consists of the following spans respectively12.0015 m, 24.140 m and 12.0015 m. spans, with a 15.240m wide bridge.

• The superstructure is supported by AASHTO Type III girders, which are continuous for live load. The substructure consists of three-column piers and abutment bents supported directly by drilled shafts. The abutment is of the semi-integral (floating) type.

Transverse section

Elevation of the bridge

Objectives of this research• The objectives of this research project are three-fold:• 1) Develop a cost-effective and aesthetically acceptable

concrete Girder with 3 spans in excess of 45 meters.• 2) Revise the New Mexico Department of Transportation

(NMDOT) with the need to build a simple girder bridge across a river, in accordance with the research and recommendations.

• 3) Develop approximate formulas to estimated Load and Resistance Factor Design (LRFD) methods.

What is LRFD & AASHTO • Load uncertainties incorporated by load factors.• Resistance factors account for the uncertainties associated with

material properties.• Load and Resistance Factor Design (LRFD).• Provides more consistent design and level of safety in th

superstructure and substructure design.• LRFD methods are used throughout this whole research project,

except where a suitable LRFD does not exist.• AASHTO is the American Association of State Highway and

Transportation Officials( Test Protocols and guidelines for highway construction and design throughout the USA)

Design steps included in the project

The following design steps are included in this example:• Concrete deck design• AASHTO Type III girder design• Bearing pad design• Pier and abutment cap design• Pier column design• Drilled shaft design• Seismic design

Superstructure Design• .

• The superstructure design includes the following elements: deck design, pre-stressed girder design, and bearing pad design. Deck design follows the NMDOT standard deck

• Girder analysis and design is performed using the computer program CONSPAN, Version 09.00.03.01. Input data and design loads needed for the computer analysis are developed and listed.

• From the resulting output, a final girder design is developed and finally the NMDOT standard beam sheet is completed.

• Reinforced elastomeric bearing pad design is also illustrated.

Bridge layout

Overall width = 15 m. Number of lanes = 3 Lane width = 3.60m. Left and Right Curbs = 0.472 m. Supplemental Layer = 0 m. Deck Thickness = 0.2286m. Haunch Thickness = 0 m. Haunch Width = 0.4064m

BeamsHeight=1143mmTop flange=406mmBottom flange=559mmmid part/web=178mmflange thickness=178mm

End and Mid-span for span 1&3

• 2 draped for the ends with a distance from the bottom 1066.8mm

• 12 straight strands at the bottom flange

• 14 Strands for the mid-span

End and Mid-span for span 2

• 6 draped strands top flange for the ends.

• 38 straight strands at the bottom of the flange

• 44 strands for the mid-span at the bottom flange

Loads on the beams

• Analysis factor on the conspan software dead loads distributed equally.

• Loads on the beams are computed and the dead loads are as shown

Shear reinforcement

• Computer Analysis results for the shear reinforcement and strand pattern are shown.

• Span 1 beam 2

Horizontal and Vertical shear reinforcement

Horizontal Shear Reinforcement

• The calculated reinforcement requirement (per meter of length) for horizontal shear is listed in the program output. Since the same reinforcement (pairs of #4 bars) will be used to satisfy both vertical and horizontal shear, the area provided is again As = 258.064 mm2

• Vertical Shear Reinforcement The computer output calculates the required reinforcing area per meter length and is listed. The computer program also allows the engineer to develop the vertical shear layout. The following shear envelopes have been developed with a pair of #4 bars for stirrups.

Substructure & Foundation designSubstructure and foundation design includes design of the piers and abutments. For thisexample the program RC-PIER, Version 09.00.03.01, will be used as the primary designaide. Refer to the preliminary design sections of this document for details of thepreliminary pier and abutment configurations.The pier is a three-column bent with circular columns that will frame directly intosupporting drilled shafts. Piers 1 and 2 bearings are fixed against longitudinal movement.

Load Combinations • This computer computer software has a list of all AASHTO LRFD loads and loads combinations.

• They are also different strengths associated with different piers.

• For Pier 1 in this example, applicable loads are DC, DW, LL, LLp, BR, PL, WA, WS, WL, and TU. EQ will not be applied in this first run.

• From the LRFD Specifications, it is determined that load cases applicable to this pier are Strength I, Strength II, Strength III, Strength V, and Service I. Extreme Event I for the 500-year flood and Extreme Event Seismic Group I will not be used for this first run.

DC: Component and attachments/Precast DC DW: Wearing surfaces and Utilities/Composite LL: Vehicular Live Load LLp: LL Permit/ Permit live BR: Braking Force/ Braking PL: Pedestrian Loads/ Pedestrian Live WA: Water and stream pressure/ Water WS: Wind and Load on structure/ Angle 0 WL; Wind Load on Live/ Angle 0 TU: Uniform Temperature/ Temperature EQ: Earthquake Effect/ Seismic

Conclusion• Satisfy all the requirements for all the loads and support requirements.• Run for 500-Year Flood (Extreme Event Group II)• Conclusion of Preliminary Design• With the check of the 500-year flood, the preliminary design work for the pier is concluded, and we

are now ready to transmit shaft loads to the Geotechnical Section for final foundation recommendations. These loads, acting at the top of shaft, are as follows (referring to the Load summary for each RC-PIER run):

• Strength Groups• • Axial Load = 3,331.71 KN• • Horizontal load = 88.96 KN• • Moment = 281.33 m• Scour depth is 3.05m• Extreme Event Seismic• Transverse• • Axial Load = 2,931.38 KN• • Horizontal load = 618.30KN• • Moment = 447.41994 KN.m• Longitudinal• • Axial Load = 2,362.01 KN• • Horizontal load = 160.14 KN• • Moment = 1,347.68KN.m• Scour depth is 0m.• Extreme Event II (500-yr flood)• • Axial Load = 2,473.21 KN• • Horizontal load = 31.14KN• • Moment = 383.70KN.m

Thank You