LENGTH LIMITATIONS OF PRESTRESSED CONCRETE GIRDER INTEGRAL ABUTMENT BRIDGES

  • : Ms Word, Ms Word Format
  • : 100 Pages
  • : ₦3000
  • : 1-5 Chapters
  •  
  • Click to DOWNLOAD Materials

LENGTH LIMITATIONS OF PRESTRESSED CONCRETE GIRDER INTEGRAL ABUTMENT BRIDGES

ABSTRACT

The construction of integral or jointless bridges in North America has become increasingly popular because of the many advantages over conventional, jointed bridges. However, conservative limits have been set on the maximum length of integral abutment bridges (IABs) because no analysis or design guidelines for IABs exist. Additionally, the behavior and potential problems associated with IABs at increased lengths are largely unknown. This study developed 3D numerical models in ANSYS that simulate IAB behavior to study the critical bridge response, establish a practical IAB maximum length, and identify potential distress in IABs at extreme lengths.

Key components to IAB behavior included in the numerical models are soil-pile interaction, abutment-pile interaction and construction joint detail. The loads on the numerical models were ambient temperature, AASHTO temperature gradient, timedependant loads, and backfill pressure. A parametric study was performed with an initial bridge length of 1000′ (305 m) considering the effects of: (1) abutment height; (2) soil stiffness; (3) construction joint flexibility; and (4) pile orientation on IAB response.    Results of the parametric study showed weak axis oriented piles developed higher pile stress than strong axis oriented piles and abutment height had the greatest effect on IAB critical response. Taller abutments, moderate construction joint stiffness, low soil stiffness and strong axis pile orientation are best suited for IABs at extreme lengths because these conditions yield comparatively lower pile stress, moment and concrete stress at the abutment-pile connection. Based on analysis results, IABs at extreme lengths develop high stress in the piles, deck, the abutment at the construction joint and the backwall-girder connection, limiting the length of IABs. A practical maximum length of 1500′ (457 m) was established based on IAB limiting factors. For IAB lengths beyond 1500′ (457 m), cracking will most likely develop at the backwall-deck connection, the abutment at the construction joint and at the abutment-pile connection. High stress, approaching yield, is also likely to develop in steel H-piles in IABs at extreme lengths.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TABLE OF CONTENTS

LIST OF FIGURES……………………………………………………………………..viii

LIST OF TABLES…………………………………………………………………………xi

ACKNOWLEDGEMENTS…………………………………………………………….…xii

 

Chapter 1 INTRODUCTION ………………………………………………………………………………………..1

1.1       Background …………………………………………………………………………………………………1

1.2Problem Statement ……………………………………………………………………………………….41.3Scope of Research ………………………………………………………………………………………..6

1.4       Objective and Tasks ……………………………………………………………………………………10

 

Chapter 2 LITERATURE REVIEW ……………………………………………………………………………..12

 

2.1       Introduction ……………………………………………………………………………………………….12

2.2       Length Limits …………………………………………………………………………………………….14

2.3        Bridge Components ……………………………………………………………………………………24

2.3.1Superstructure ………………………………………………………………………………… 242.3.2Girder to back-wall connection …………………………………………………………. 262.3.3Backwall – Approach Slab ……………………………………………………………….. 27

2.3.4        Abutment……………………………………………………………………………………….. 28

2.3.5       Piles ………………………………………………………………………………………………. 31

2.4       Soil-Structure Interaction …………………………………………………………………………….33

2.4.1       Abutment-backfill interaction …………………………………………………………… 34

2.4.2       Soil-pile interaction …………………………………………………………………………. 34

2.5       Thermal Effects ………………………………………………………………………………………….35

2.5.1       Ambient Temperature ……………………………………………………………………… 36

2.5.2       Temperature Gradient ……………………………………………………………………… 38

2.6Time dependant effects ……………………………………………………………………………….392.7Coefficient of Thermal Expansion ………………………………………………………………..41

2.8       Modeling Methodologies …………………………………………………………………………….43

 

Chapter 3 NUMERICAL MODEL ……………………………………………………………………………….46

 

3.1       Introduction ……………………………………………………………………………………………….46

3.2Bridge Geometry ………………………………………………………………………………………..473.3Study Model ………………………………………………………………………………………………50

3.4       Material Properties ……………………………………………………………………………………..54

3.4.1        Bridge Components ………………………………………………………………………… 54

3.4.2        Bearings ………………………………………………………………………………………… 55

3.5       Loads ………………………………………………………………………………………………………..56

3.5.1       Ambient Temperature Load ……………………………………………………………… 56

3.5.2       Temperature Gradient ……………………………………………………………………… 57

3.5.3       Time-Dependant Loads ……………………………………………………………………. 58

3.6Construction Joint ………………………………………………………………………………………593.7Soil- Pile Interaction …………………………………………………………………………………..60

3.8       Backfill Pressure ………………………………………………………………………………………..62

3.9       Parametric Study ………………………………………………………………………………………..64

 

Chapter 4 PARAMETRIC STUDY RESULTS …………………………………………………………………67

 

4.1       Introduction ……………………………………………………………………………………………….67

4.2        Pile Displacement ………………………………………………………………………………………68

4.3Max Stress in Piles ……………………………………………………………………………………..724.4Pile Moment ………………………………………………………………………………………………764.5Concrete Stress at Abutment-Pile Connection ………………………………………………..80

4.6        Girder Bottom Stress…………………………………………………………………………………..84

4.7        Other Bridge Components …………………………………………………………………………..88

4.7.1       Reinforcing Bars at Construction Joint ………………………………………………. 88

4.7.2       Abutment Concrete Stress at Construction Joint …………………………………. 89

4.7.3       Girder-Backwall Connection ……………………………………………………………. 90

4.7.4Transverse Threading………………………………………………………………………. 914.7.5Elastomeric Bearing ………………………………………………………………………… 93

4.7.6       Deck ……………………………………………………………………………………………… 94

4.8       Discussion of Results ………………………………………………………………………………….95

4.8.1       Abutment Height …………………………………………………………………………….. 96

4.8.2Soil Stiffness ………………………………………………………………………………….. 994.8.3Construction Joint Stiffness ……………………………………………………………. 1034.8.4Pile Orientation …………………………………………………………………………….. 106

4.8.5       Summary ……………………………………………………………………………………… 107

 

Chapter 5 LENGTH LIMITS ……………………………………………………………………………………109

 

5.1Introduction ……………………………………………………………………………………………..1095.2Bridge Configuration ………………………………………………………………………………..109

5.3Length Models …………………………………………………………………………………………1115.4Maximum Pile Stress ………………………………………………………………………………..1125.5Concrete Stress at Abutment-Pile Connection ………………………………………………115

5.6       Construction Joint …………………………………………………………………………………….118

5.6.1       Reinforcing Bars …………………………………………………………………………… 118

5.6.2        Abutment……………………………………………………………………………………… 120

5.7       Deck ……………………………………………………………………………………………………….122

5.8        Girder Stress…………………………………………………………………………………………….124

5.9        Stress in Girder at Transverse Threading Location ……………………………………….125

 

Chapter 6 SUMMARY, CONCLUSION AND RECOMMENDATION ……………………………………127

 

6.1Summary …………………………………………………………………………………………………1276.2Conclusions ……………………………………………………………………………………………..128

6.3        Design Recommendations …………………………………………………………………………130

6.4       Recommendations for future research …………………………………………………………131

 

REFERENCES……………………………….……………………………………………133

Chapter 1                                                    

INTRODUCTION

1.1     Background

For many years transportation agencies have endured considerable problems associated with the use of expansion joints in conventional jointed bridges. These expansion joints and bearings are used to accommodate the expansion and contraction of the superstructure due to thermally induced loads and time dependent effects such as creep and shrinkage.

Over time, expansion joints tend to leak and are largely responsible for the deterioration of bridge bearings and supporting structure from de-icing chemicals. Debris also tends to become lodged in expansion joints restricting intended movement. Retaining hardware for joints can also become loosened by snowplows and repeated vehicular impact posing a potential risk to motorists. Support bearings designed in conjunction with expansion joints are typically a significant initial investment and are costly to install, maintain and replace. Most bearings eventually rupture, split, or fail as a result of corrosion or loss of lubrication. As a result, bridge elements can become overstressed or damaged.

IABs are steadily becoming more popular among bridge owners. IABs remain in service longer with only moderate maintenance and occasional repairs required (Burke 1990). Now, at least 40 states have adopted some form of integral or semi-integral bridge design. In 2004, a survey was conducted by the Federal Highway Administration (FHWA) and the Constructed Facilities Center (CFC) at West Virginia University (WVU), to determine the usage and design of Integral Abutment and Jointless Bridges

(IAJB) in the United States. The IAJB 2004 survey was distributed to all 50 States’

Department of Transportation (DOT), DC DOT, Puerto Rico Highway and

Transportation Authority, and the Federal Lands Highway Division. Thirty-nine of fiftythree (74%) agencies responded and reported that there are approximately 13,000 integral abutment bridges in-service, of which there are more than 9,000 fully integral abutment bridges (Maruri et.al., 2005). Based on the information received from the survey conducted by the FHWA and by Kunin and Alampalli (2000), Table 1.1 summarizes the

design criteria for full integral bridges.

Table 1.1 Range of Design Criteria for Prestressed Concrete IABs (Maruri et.al., 2005)

Parameter  Range
Maximum Span 60 – 160 ft (18-49 m)
Total Length 150 – 1175 ft (46-358 m)
Maximum Skew* 45º
Maximum Curvature 0-10º

*Measured from a line perpendicular to the bridge axis.

The design and analysis of IABs are more difficult than that of conventional jointed bridges due to (1) difference in boundary conditions, (2) uncertainties of loads and material properties, and (3) nonlinearities in the factors affecting the bridge behavior (Kim 2009). These factors include:

  • annual and diurnal temperature fluctuations;
  • creep and shrinkage; and
  • non-linear soil-structure interaction

Because of complex IAB behavior, short and long-term response is more difficult to predict and consequently, a relatively conservative approach to design and analysis has been adopted by state Department of Transportations (DOTs).

Presently, the American Association of State Highway and Transportation Officials Load and Resistance Design Manual, AASHTO LRFD (2008), has no analysis or design guidelines for IABs and no recommendations on the maximum length of IABs. Therefore, length limits in most states are based on performance of in-service IABs. There is a need for further research into the behavior of IABs at extreme lengths and the development of design standards that address the problems encountered in the design and detailing of these bridges.

Tennessee has the longest set limit of 800 ft (244 m) for prestressed concrete girder IABs. However, Tennessee also holds the record for the longest IAB constructed, which has a length of 1,175 ft (358 m). States such as Colorado and Oregon also built IABs greater than 1000 ft (305 m) with lengths 1,112.9 ft (339m) and 1,100.7 ft (336m) respectively.

The present study identifies stress development at critical locations and examines potential distress at these locations. This will be done through the development of numerical models using previously established modeling methodologies to investigate the behavior of IABs at extreme bridge lengths, i.e. beyond 1000 ft (305 m). The use of numerical models has been proven to predict, with high accuracy, the response of IABs. As a result, the modeling techniques developed in previous research studies can be used to investigate the behavior and identify potential areas of distress in IABs at increased lengths.

 

1.2     Problem Statement

IABs are typically comprised of single or multiple-spans built without expansion joints. The end girders are cast integrally with the back-wall and usually have a continuous deck from one abutment to the other. The response from both primary and secondary loads must be accommodated by other means because there are no expansion

joints.

Primary loads are applied directly to the bridge structure and are typically accounted for in the initial design; these include, dead, live, snow and wind loads. Additional secondary loads resulting from the bridge response to external or internal changes over time: (1) temperature-induced expansion/contraction, (2) differential settlement, (3) thermal gradients and (4) creep and shrinkage (Hassiotis and Roman 2005), are not usually accounted for in the initial design. These secondary loads can result in stresses comparable to those caused by gravity loads.  For example, the Pennsylvania Department of Transportation (PennDOT) specifies that these superimposed forces (creep, shrinkage and thermal gradient) should be considered for concrete structures exceeding 600 ft (244 m).

Daily and seasonal temperature changes impose cyclic displacements on the bridge superstructure and ultimately on the abutments, backfill and steel H-piles. These displacements are a function of temperature fluctuations, material properties and structure length. Therefore, as IABs increase in length they are subjected to a larger response. The increased bridge response can cause serious damage if not properly accounted for. These IABs may experience:

  • distress at the abutment-pile location;
  • increased moment and stress in piles;
  • distress at the backwall-abutment connection; and
  • increased concrete stresses at connections such as: girder-backwall , deck- abutment, etc

The maximum permitted IAB length varies from state to state and is usually limited by the maximum thermal movement allowed and empirical data collected from in-service IABs. Because conservative limits have been set on the maximum length of IABs, behavior and potential problems at increased lengths are still unknown. A thorough understanding of IAB behavior at longer lengths and practical limits on the length of the structure are imperative to quality long term performance of the structure. Some issues of concern are:

  • the range over which empirical data can be extended before additional

analysis is required;

  • orientation of the steel H-piles;
  • effect of larger bridge response on the backwall-abutment connection; geometric,  material and geotechnical properties affecting IAB behavior; and
  • need for additional/alternate design of bridge components.

 

1.3     Scope of Research

Field data collected over a seven (7) year period from instrumented bridges along the I-99 extension in central Pennsylvania have been used in previous studies to calibrate numerical models and refine modeling techniques to predict the behavior of IABs. The numerical model methodologies were used to develop models to:

  • compare predicted and measured response of IABs;
  • evaluate the superstructure stresses;
  • simulate hysteresis behavior; and
  • develop load and resistance factors for IAB design.

These studies have:

  • validated the use of numerical modeling for use in predicting both the shortterm and long-term behavior of IABs;
  • shown a close correlation between the predicted response of both 2D and 3D models;
  • developed methods to accurately simulate loads and bridge component behavior and;
  • identified key factors affecting bridge behavior.

This study investigates IAB behavior at extreme lengths using numerical models developed using modeling techniques established in previous studies.  Each bridge model used in this study has four prestressed, BT-72 girders spaced at 12′-0″ (3.7 m) that support a 9″ (229 mm) thick, cast-in-place, concrete deck. A typical IAB cross-section is shown in Figure 1.1. The bridge models are symmetric about the longitudinal and transverse axes and do not include skew end supports. Half of the IAB is modeled with equally spaced pier supports, as shown in Figure 1.2. An abutment height of 9′-0″ (2.7 m) was used in the initial model and altered in the parametric study, shown in Figure 1.3. The abutments are supported by 8 steel HP12x74 (HP310x110) piles embedded 2′-0″ (0.61 m) into the abutment and supported by a single layer of soil, above the water table, and driven to bedrock. The typical backfill material, an open graded sub-base (OGS) coarse aggregate, used by the Pennsylvania Department of Transportation was adopted in this study.

Figure 1.1 Typical Cross Section of IAB

 

Figure 1.2 Typical Elevation of Bridge Considered in Numerical Model

 

Figure 1.3 Section of Integral Abutment

This study utilizes the commercially available software ANSYS, to develop 3D numerical models. The loads used in the applied to the numerical model are:

  • temperature range using Procedure A for moderate climates recommended by AASHTO LRFD (2008);
  • temperature gradient using Zone 3 positive and negative temperature values recommended by AASHTO LRFD (2008);
  • time dependant effects, creep and shrinkage coefficients recommended by

AASHTO LRFD (2008); and

  • backfill pressure on abutment using open graded sub-base (OGS) coarse aggregate; and
  • soil pressure on piles using defined soil properties from soil reports of monitored bridges.

IAB structures experience two types of non-linearity: (1) geometric; and (2) material. These nonlinearities are a result of concrete cracking, non-linear soil response, and non-linear behavior at the abutment construction joint. The IAB response of the models in this study is expected to be non-linear due to these factors.  For the purpose of this study, the non-linear soil response and abutment connections were considered while the material properties were considered to be linearly elastic-perfectly plastic.

This study investigated the effects on: (1) pile head displacement; (2) maximum pile stress; (3) maximum pile moment; (4) concrete stress at abutment-pile location; and (5) girder bottom stresses. In addition to bridge response, this study also investigates potential distress and failures at the following locations:

  • girder-backwall contact;
  • girder bearings;
  • construction joint; and
  • abutment-deck connection.

A parametric study was performed varying four bridge parameters. Three different abutment heights were investigated with heights 4′-0″ (1.2 m), 9′-0″ (2.7 m) and 12′-0″. The pile orientation was varied between strong and weak axis bending and stiff clay, medium clay and sand were used for the soil types. The influence of the construction joint stiffness was also investigated in this study. The connections considered were (1) pinned, (2) PennDOT Standard #5 U shaped bars @ 9″ spacing (#25 mm bars @ 229 mm); and (3) rigid connection. Both expansion and contraction cases were considered in this study.

The material and soil properties used in the bridge models were adopted from field data collected from monitored bridges in Pennsylvania (Laman et al. 2006). The bridge model responses were examined and compared to AASHTO LRFD (2008) limits. Ultimately, the maximum length of IABs is established based on the configuration that yields forces and stresses within the established AASHTO limits.

 

1.4     Objective and Tasks

The overall objective of this study is to establish length limits for IABs when subjected to thermal and time dependant loads. Additionally, this study provides design recommendations for longer IABs. The tasks to be completed toward the objective are:

  1. develop numerical models of an IA bridge using previously developed modeling techniques and applied loads; and
  2. perform a parametric study varying the geometric and material properties.

The numerical model developed in this study identifies critical locations of high stresses and provides a better understanding of bridge behavior under thermal and timedependant loads. Initially, a 1,000 ft (305 m) IAB, is modeled and is used in identifying the high stress locations on the bridge superstructure and substructure. The initial bridge length is selected based on length limits of in-service IABs. A parametric study is performed to establish the contribution of specific bridge parameters to the development of stresses at critical bridge locations. The bridge configuration that experiences comparably lower stresses is used to establish a practical maximum length. From these tasks, the objectives of this study are:

  1. identify the primary limiting factor for IAB length;
  2. establish a practical IAB length limit; and
  3. suggest alternate construction and/or details.

LENGTH LIMITATIONS OF PRESTRESSED CONCRETE GIRDER INTEGRAL ABUTMENT BRIDGES

Sharing is caring!

Leave a Reply