Attch_4_Basis_of_Design-Upper_El_Rancho.pdf

BASIS OF DESIGN

DESIGN OF REPAIRS FOR THE UPPER EL RANCHO ROAD BRIDGE

(VAFB FAC # 1910)

Vandenberg Air Force Base, California

Project No.: VAND-12-S-3625

Contract No.: FA 8903-08-D-8770

Project Manager: Rob Schroeder

Contracting Officer: Toby Carnes

Contracting Officer Representative: Jordan Hampton

Prepared by:

999 Town & Country Road Orange, CA 92868

Contact: Kosal Krishnan Tel: (714) 567-2463 Fax: (714) 567-2441

May 14, 2013

ATTCH 4: FA4610-14-R-0032

May 14, 2013 Design of Repairs for the Upper El Rancho Road Bridge

Basis of Design i

Table of Contents

Executive Summary ................................................................................................................. iii

I. Introduction

II. Site Location

III. Bridge Description

IV. Prior Inspections and Evaluations

V. Site Visit and Inspection

VI. Geology

VII. Repair and Retrofit Criteria

VIII. Seismic Design Criteria

IX. Analysis Approach

X. Analysis Results

XI. Conclusions and Retrofit/Repair Recommendations

XII. Construction Requirements

XIII. Cost Estimate

Basis of Design ii

List of Appendices

A1 Photographs

A2 Geotechnical Memorandum

A3 Analysis Summary Tables (As-Built Condition)

A4 Repair/Retrofit Cost Estimate

A5 Table of Contents for Drawings and General Plan

A6 Support Information and Client Direction

A7 List of Recycled Materials

A8 Inventory and Load Study

A9 Technical Field Investigation

A10 Design Calculations Volume 1: Seismic As-Built Analysis and Evaluation

A11 Design Calculations Volume 2: Bridge Retrofit and Repair

Basis of Design iii

Executive Summary

The Upper El Rancho bridge is a 3-span bridge, built in 1962 and located at Vandenberg Air Force Base.

The bridge carries two lanes of traffic over Union Pacific Railroad (UPRR) tracks. Previous inspections and evaluations of the bridge occurred between September 2007 and October 2010. Various deficiencies and maintenance issues were identified as part of these previous investigations.

The purpose of the project is to develop plans, specifications, and cost estimates detailing the repairs and seismic retrofit required for the Upper El Rancho Road Bridge. The project also included the following tasks: bridge inspection, preparation of a geotechnical memorandum from existing boring logs, and seismic analysis and evaluation.

AECOM conducted a bridge inspection on November 7, 2012. The structure is rated in Fair condition overall and all primary elements are structurally sound. The following repairs and upgrades were suggested: repair spalled and delaminated concrete on the north and south face of cap beam at Bent 3, repair spalled and delaminated concrete at span 2, and upgrade bridge barriers and guardrails. Additional considerations are to continue to perform routine inspection on a 24 month frequency and monitor cracks in Span 2.

Seismic analysis and evaluation is performed based on conventional seismic analysis methodology which includes the following: a linear dynamic analysis to determine displacement demands and a non-linear static analysis to evaluate displacement capacities. The results of the analysis demonstrates that the existing bridge meets most current seismic requirements. No retrofit is required, but it is recommended that the seats that support Span 2 be extended to current standards and that transverse shear keys be installed to limit differential transverse movement of the middle span.

The following is a summary of recommended bridge repairs and retrofits:

1. Increase the pier seat width: This work will consist of increasing the seat width by at least 1 ft at Bent 2 and Bent 3. Reinforcing dowels will be drilled into the face of the existing bent cap face. Additional bar reinforcing will be placed within the seat extension prior to concrete placement.

2. Install transverse shear keys at the bents: This work will consist of forming 1 ft wide shear keys at Bent 2 and Bent 3. A total of 2 shear keys are required at each bent. Reinforcing dowels will be drilled into the existing concrete surface. Additional bar reinforcing will be placed within the shear key prior to concrete placement.

3. Patch and repair spalled concrete: Unsound concrete will be removed to expose sound hard concrete substrate. Existing reinforcement will be protected in place and cleaned for rust. A Portland Cement Concrete patch will be placed to match the original concrete surface. Patch and repair is required at Bent 3 and at one location along the face of girder at Span 2.

4. Replace existing barrier with a new Type 732 barrier: The existing curb and railing will be removed along with adjacent asphalt concrete surfacing. Reinforcing dowels will be drilled into the bridge deck. At Span 2 a concrete overlay will be placed. Additional bar reinforcing will be placed within the barrier prior to concrete placement.

5. Replace approach Metal Beam Guard Rail

6. Replace the corroded utility hangers

Basis of Design iv

The design of the retrofit and repair work conforms to AASHTO LRFD Design Specifications, 4th edition and the Caltrans amendments. Reinforced concrete design is based on a nominal concrete strength of 3.6 ksi and reinforcement yield strength of 60 ksi. Structural steel design for utility hangers is based on a yield strength of 36 ksi. Barrier collision loads are based on a 54 kip maximum traffic impact loading per the AASHTO LRFD Design Specification.

Basis of Design 1

II. Introduction

This report has been prepared for and contains the basis of design for the Design of Repairs for the Upper El Rancho Road Bridge (VAFB Facility No. 1910) project. This project calls for the inspection and review of the existing bridge along Upper El Rancho Road over the Union Pacific Rail Road (UPRR) railroad and development of plans, specifications, and cost estimates detailing the repairs and seismic retrofit required.

III. Site Location

The project site is located in the northern portion of Vandenberg Air Force Base (AFB) which is situated along the coast of California between Santa Maria and Santa Barbara, near Lompoc. El Rancho Road travels predominantly north south between the main portion of the AFB and terminates at Point Sal Road. The bridge is located just before the road merges into Point Sal Road.

Upper El Rancho Road Bridge

UPRR Rail Road

Santa Maria

Basis of Design 2

IV. Bridge Description

General Arrangement

The Upper El Rancho Road Bridge (Bridge No. VAFB-FAC#1910) is a 3-span bridge which carries Upper El Rancho Road over Union Pacific Railroad (UPRR) tracks. The bridge, constructed in 1962, measures 159’-4”+ in length and 30’-0”+ in width and supports two lanes of opposing traffic. Each of the two abutments and two bents are positioned along a 37o50’09” skew.

Superstructure

Two superstructure types are used for the Upper El Rancho Road Bridge. The two end spans are cast-in-place T-Girders which were integrally cast with the bent caps and abutment diaphragms.

The center span is made up of precast, prestressed box girders which are simply supported at each bent.

The cast-in-place concrete T-Girder end spans are approximately 45’-8” and 50-4”, respectively.

Each of the six girders have a total depth of 3’-9” and width of 1’-6” with the deck measuring 6” thick. Intermediate diaphragms are provided at roughly the midspan of each cell.

The 61’-2”+ long center span is made up of 7 precast, prestressed concrete box girders placed side by side. Each box measures 4’-0” wide by 2’-9” deep with top slab, bottom slab, and web thicknesses of 6”, 4.5”, and 4.5”, respectively. Two intermediate diaphragms are placed along the length of the box to tie adjacent boxes together with #8 tie rods. The boxes sit on seats cast into the bent caps and are held in place by #8 dowels.

Substructure

The substructure consists of two multi-column bents and two abutments. Each bent consists of a cap beam to provide an integral connection between the superstructure and six 2’-4”+ diameter columns. The abutments are similar to bents with a diaphragm cast to provide an integral connection between the superstructure and five 2’-4”+ diameter abutment columns. Both the abutment and bent columns are founded on sub-grade bell footings. The bell footing is 4’-8”+ in diameter for each bent column and 4’-2”+ in diameter for each abutment column.

The as-built plans specify that the bent and abutment footings are a minimum of 15.5 ft+ beneath the existing grade and depict bottom of the footing elevations as EL 237ft+ for the bents and 235ft+ and 240ft+ for Abutments 1 and 4, respectively. They also indicate that the embankments installed at each abutment were constructed simultaneously with the bridge.

V. Prior Inspections and Evaluations

The Upper El Rancho Road bridge was previously analyzed in 2007 by Bengal Engineering, Inc.

The “Structural Analysis of Upper El Rancho Bridge” study included a detailed inspection of the structure which was conducted on September 20, 2007. The aforementioned report noted the following list of existing deficiencies:

Approach and bridge railings do not comply with current AASHTO standards

Basis of Design 3

Curbs are not structurally adequate Observed concrete cracking and spalls have lead to rebar corrosion Corroded water line and support hangers Shear reinforcement do not meet current maximum spacing requirements Superstructure shear and flexural capacity is not sufficient for special payloads Insufficient pier seat width Bent columns do not meet local displacement ductility requirements Insufficient lateral seismic resistance of the middle span

A follow up inspection took place on October 28, 2010 by Bengal Engineering, Inc. The results of this inspection agreed with those of the previous inspection and evaluation that was completed in 2007. The report concluded the bridge was in “Fair” condition and recommended the following repairs:

Remove delaminated and spalled concrete, clean exposed and corroded rebar and patch.

Replace damage bridge rail and upgrade system to include guardrail end treatments and rail transitions.

Clean and repaint utility hangers and bridge railing.

VI. Site Visit and Inspection

As part of the kick-off meeting for this project, a site visit took place on October 4, 2012.

An inspection was completed to confirm findings noted in previous inspections as well as to note any additional deficiencies that may have developed since the last inspection. This inspection took place on November 7, 2012 and confirmed the observations noted in the 2007 and 2010 inspection reports. No additional deficiencies were noted. See Appendix A1 for site visit and inspection photographs.

VII. Geology

Bridge Name Soil Material

Groundwater Depth

Foundation Type

Max EQ/ Accel Max ARS

Upper El Rancho Road

Medium Dense to

Very Dense Sand

31 ft to 47 ft below grade.

Sub-grade Bell Footings

MCE Magnitude 6.6 Max. Bedrock Acceleration

0.514g

1.000g

Notes:

1. Draft geotechnical memo is included in Appendix A2

VIII. Repair and Retrofit Criteria

The repairs and retrofit measures specified in this document are intended to preserve or upgrade the structure to meet current life safety requirements and prevent structural collapse under everyday use of the structure and in the event of a maximum credible earthquake (MCE). All

Basis of Design 4 recommended repairs are specified to maintain the structural integrity of the bridge structure.

The design of the retrofit and repair work will conform to AASHTO LRFD Design Specifications, 4th edition and the Caltrans amendments. Specific criteria for the repair and retrofit work is as follows:

Reinforced Concrete for Seat Extension, Shear Keys and Barrier Replacmement:

Normal Weight Concrete - Unit weight: 150 pcf

Light Weight Concrete - Unit weight: 115 pcf fy = 60 ksi f’c = 3.6 ksi fye = 68 ksi f’c = 5.0 ksi

Structural Steel for Utility Hangers:

Unit weight: 490 pcf fy = 36 ksi

Barrier Replacement Loads:

Vehicular Collision Force (CT): 54 K maximum traffic impact loading evenly distributed over 10 ft at top of barrier and 1:1 distribution down and out. (Per Caltrans Standard Drawing XS 16-045)

IX. Seismic Design Criteria

A. References

Ref.

No

Organization Reference

1 Caltrans Bridge Design Specifications (LFD) 2 Caltrans Seismic Design Criteria (SDC) version 1.6 3 Caltrans Bridge Design Aids (BDA) 4 Caltrans Memo to Designers (MTD) 5 Caltrans Standard Plans 2010 Edition 6 Caltrans Cost Data Book (2011)

B. Materials

Material properties were not specified on the available as-built plans. Therefore, the following properties were assumed.

Basis of Design 5

Material Property Description

Cast-in-place Concrete f’c = 3,000 psi Concrete compressive strength at 28 days Ec = 3,122,000 psi Elastic modulus of concrete f’ce = 5,000 psi Expected concrete compressive strength Ece = 4,030,000 psi Expected elastic modulus of concrete

Precast Concrete f’c = 5,000 psi Concrete compressive strength at 28 days Ec = 4,030,000 psi Elastic modulus of concrete f’ce = 6,500 psi Expected concrete compressive strength Ece = 4,596,000 psi Expected elastic modulus of concrete

Reinforcing Steel (Grade 40) fy = 40,000 psi Specified minimum yield strength fye = 44,000 psi Expected yield strength fu = 60,000 psi Specified minimum tensile strength fue = 66,000 psi Expected tensile strength

Es = 29,000,000 psi Elastic modulus of reinforcing steel

C. Design Loads The structural loading criteria was applied in accordance with LFD and as described below.

Dead Loads

The following unit weights were assumed for all existing and proposed materials.

Material Unit Weight Description Cast-in-place Concrete 150 pcf Used for all cast-in-place concrete Precast Concrete 150 pcf Used for all precast concrete Reinforcing Steel 490 pcf Used for all reinforcing steel Structural Steel 490 pcf Used for piping, hangers, and other steel components Asphalt 140 pcf Used for bituminous fill and wearing surface Soil 120 pcf Used for all soil fills Water 62.4 pcf Used for utility weight

Live Loads

Load rating analysis is not within the scope of work for this project. However, as part of the 2007 Bridge Evaluation completed by Bengal Engineering, Inc., the structure was rated for HS20 trucks, P13 permit vehicles, and a number of Client supplied vehicles. A list of vehicles studied in this evaluation is shown below.

HS20

P13 (Permit Load) Unladen

LGM_30G

Minuteman Peacekeeper 1 ASTS Type-2 LTV

MDA_120_1

Basis of Design 6

MDA_120_2

MDA_110

TENDER 5 (Water Tanker Fire Rescue Truck)

The aforementioned study showed that the bridge structure has an inventory rating less than 1.0 for most vehicles. However, the bridge has an Operating Rating of more than 1.0 for all vehicles except the P13, Peacekeeper and 1 ASTS Type-2 LTV.

Seismic Loads

The following acceleration response spectrum was used to evaluate the bridge structure response and components.

Period (sec) Acceleration (g) 0 0.514

0.1 0.726

0.2 0.925

0.3 1.000

0.5 0.992

1.0 0.822

2.0 0.530

3.0 0.328

4.0 0.222

5.0 0.165

D. Foundation

The following parameters were used to evaluate the foundation capacities of the structure.

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Sp ec tr al

A cc el er at io n (g

Period (sec)

ARS Curve for Upper El Rancho Bridge PGA=0.514g

Basis of Design 7

Item Value Description

Pile Capacity

50 kips Allowable load capacity in compression for bent piles 150 kips Ultimate load capacity in compression for bent piles 10 kips Ultimate load capacity in tension for bent piles

100 kips Allowable load capacity in compression for abutment piles 300 kips Ultimate load capacity in compression for abutment piles 150 kips Ultimate load capacity in tension for abutment piles

Fixity Depth 8.3 x pile diameter Upper bound equivalent fixity depth of abutment columns.

5.4 x pile diameter Lower bound equivalent fixity depth of abutment columns.

Lateral Soil Pressure

0.3 Active lateral soil pressure coefficient

3.0 Passive lateral soil pressure coefficient

X. Analysis Approach

A. As-Built Analysis

The intent of the as-built analysis is to evaluate the structure in its existing condition in order to determine the structural deficiencies that require retrofit. The as-built analysis calculations can be found in Appendix A10. The structure was modeled in its as-built condition with consideration given to any damage observed in the structural components during structural inspections.

The following procedure was followed to evaluate the existing structure.

Review bridge as-built plans, inspection reports, geotechnical reports and perform inspection and geotechnical investigations as needed.

Perform seismic analysis o Perform displacement demand analysis of entire structure using SAP2000, CSI Bridge or hand calculations.

o Perform moment-curvature analysis using Xtract or Xsection.

o Perform seismic assessment of existing structures.

o Perform static nonlinear (pushover) analysis using SAP2000 or CSI Bridge if warranted by preliminary analysis.

o Determine displacement ductility capacity, displacement ductility demand, and displacement D/C ratio for capacity protected members.

o Evaluate whether further analysis is required to address P- concerns.

Check substructure details using analysis results o Bent Cap and Abutment Diaphragm o Columns o Footings o Seat width and/or connection strength.

Identify and list structural deficiencies

B. Retrofit and Repair Analysis/Calculations

The intent of the retrofit analysis is to verify that the proposed retrofit measures successfully address the deficiencies identified in the as-built analysis. Repair calculations include the barrier

Basis of Design 8 replacement and the waterline utility hangers. The retrofit and repair calculations can be found in Appendix A10.

XI. Analysis Results

A. As-Built Analysis

Overview

The 159’-4”+ bridge structure supported on 2 multi-column bents was assessed and evaluated for seismic retrofit.

The structure is assumed to respond as a frame in both the transverse and longitudinal directions.

The bridge structure was originally designed in 1961. The actual material properties are not specified in the available as-built plans but are assumed as nominal concrete strength f’c=3,000psi and Grade 40 reinforcement.

Each column is supported by bell footings embedded a minimum of 15.5ft below the finished grade. The column longitudinal bars are terminated above the bell footing. The confinement reinforcement for the column longitudinal bars is #4 spirals at a 2.5 inch pitch.

A summary of key properties and dimension for the structure is provided in Table 1 in Appendix A3.

Seismic Performance Assessment

The first step in the seismic evaluation of the existing bridge structure was the capacity assessment of the frame in the longitudinal and transverse directions. Plastic hinges were expected to form at the top of the bent columns and at both the top of column and the fixity depth below grade for abutment columns. The load/deflection behavior of the individual column and of the frame was developed. The expected properties listed above were assumed as the most likely material properties for the structure.

Moment Curvature Analysis

As-built plans indicate that the columns are confined by No.4 spirals at a 2.5in pitch.

The moment-curvature analysis was performed using the computer program Xtract. The expected concrete material property f’ce=5,000 psi with a maximum concrete compressive strain of 0.005 was used. The expected steel material properties used in the analysis are fye= 44,000 psi, fue= 66,000 psi; sh = 0.0195, and the su

R = 0.09. An idealized bilinear elasto-plastic moment curvature relationship was established by extrapolating first reinforcement yield to the probable moment capacity level or yield moment My. The yield curvature, plastic curvature, yield moment, as well as effective moment of inertia is provided in Table 2A and Table 2B in Appendix A3 for abutment and bent columns, respectively.

Column plastic hinge rotations and local ductility were established per Caltrans SDC 3.1. For the longitudinal direction it was assumed that the columns were subject to dead load only. For the transverse direction, the column axial load included the effects of overturning. Since the

Basis of Design 9 displacement capacities are much less than those specified in Caltrans SDC, a pushover analysis is not warranted for this structure. Therefore the overturning loads were estimated using hand calculations.

Boundary Condition Evaluation

The abutment and bent columns are supported on sub-grade bell footings. These footings are located at depths of about 36.5 ft, 15.5 ft, and 38.9 ft for Abutment 1, Bents 2 and 3, and Abutment 4, respectively. Since the embedment depth varies substantially between the bents and the abutments, it was important to evaluate each boundary condition independently.

An L-Pile model was run for the abutment and bent columns to determine if adequate embedment was provided to achieve fixity. The analysis showed that the abutment column would achieve fixity between the depths of 5.4 and 8.3 times the column diameter. An upper bound pile fixity condition of 9 times the pile diameter was conservatively applied for all abutment piles in this analysis.

The bent columns were found to have inadequate embedment to achieve fixity. The columns were found to rotate about the column bottom under lateral loads. Therefore, a pinned condition was assumed at the base of all bent columns. Furthermore, since the column reinforcement terminates just above the bell footing and there is no way to transfer moments into the foundation, it was assumed that a pin condition would develop just above the bell footing.

Column longitudinal reinforcement extends into superstructure close to top of deck with embedded depth of approximately 2‘-4” and 2’-0” at the abutment diaphragm and bent cap, respectively. Full moment capacity of all columns is expected to be developed.

Seismic Analyses

A 3D model has been developed to study seismic performance of the Upper El Rancho Road bridge using SAP2000. Columns, superstructure and cap beam elements were modeled as frame elements. As previously mentioned the abutment columns were fixed at a depth of 9 times the diameter of the column and the bent columns were pinned at the top of the bell footing.

The results of the response spectra analyses were used to estimate seismic displacement demand.

Model Summary

Effective “Cracked” stiffness for the columns, bent caps, and abutment diaphragms were established based on Xtract runs.

The structure was analyzed with ground motions applied in the longitudinal and transverse directions (parallel and perpendicular to the bridge alignment) as well as both parallel and perpendicular to the bent skew. In addition, the 30% orthogonal load contribution strategy was applied for both the longitudinal and transverse directions.

The linear elastic model included the effective abutment stiffness, keff, perpendicular to the abutment diaphragm that accounted for the embankment fill response. The maximum passive pressure of 5 ksf was adjusted using height proportionality factor h/5.5ft.

Since the abutments behave as a bent and have stiffness contributions due to frame action, no transverse springs were applied at the abutments.

The column fixities were examined in detail and are modeled as described in previous sections.

Basis of Design 10

The superstructure was modeled to rigidly connect the end spans (Spans 1 and 3) with the adjacent abutment and bent. The center span (Span 2) was modeled with pin connections to the adjacent bents.

Modal Analysis Results

The dynamic behavior of the structure was dominated by one mode in each of the longitudinal and transverse directions as summarized in the following table.

Predominant Modes

Mode Period (seconds)

Mass Participation Mode TypeLongitudinal Transverse

1 0.67 16.8% 73.2% Transverse 2 0.49 77.1% 14.2% Longitudinal 3 0.35 93.48% 0.18% Torsional

Total modal mass participations of 98% and 94% were recorded in the longitudinal and transverse directions, respectively.

Seismic Displacement Demands

Maximum displacement demands of 3.1” and 4.8” were recorded for the bent columns in the longitudinal and transverse directions, respectively. The seismic displacement demands for bent columns are summarized in Table 3A and Table 3B in Appendix A3 for longitudinal and transverse directions, respectively.

Seismic Performance Assessment

The following sections provide a rough summary of findings for displacement ductility, P-effects, and column shear.

Displacement Ductility

The displacement ductility of the abutment and bent columns were checked in accordance with Caltrans SDC. Local displacement ductility was evaluated per SDC 2.2.3, displacement ductility demand was verified per SDC 3.1.4, and displacement demand-capacity ratios were checked per

SDC 4.1.1.

The displacement ductility demands range from 0.2 to 0.3 and 0.4 to 0.5 for bent columns in the longitudinal and transverse directions, respectively. All cases are better than the maximum displacement ductility of 5.0 per current Caltrans SDC for multi column bents. See Table 3A and Table 3B in Appendix A3 for a summary of displacement ductility demands for bent piles in the longitudinal and transverse direction, respectively.

The displacement demand-capacity ratios are less than 0.1 for bent columns in both the longitudinal and transverse directions. All cases are better than the maximum demand-capacity ratio of 1.0 per current Caltrans SDC. See Table 3A and Table 3B in Appendix A3 for a summary of demand-capacity ratios for bent piles in the longitudinal and transverse direction, respectively.

There are no displacement ductility concerns for the Upper El Rancho Road bridge structure.

Basis of Design 11

P- Effect

The effects of P- were evaluated in accordance Caltrans SDC 4.2. The P- / Mp ratios for bent columns were less than 0.1 for both the longitudinal and transverse directions. The ratios are less than the allowable tolerance of 0.2 set forth in Caltrans SDC for which P- effects can be neglected. P- check results for bent columns are summarized in Table 4A and Table 4B in Appendix A3 for longitudinal and transverse movement, respectively.

Column Shear Strength

The shear strength of abutment and bent columns were checked in accordance with Caltrans SDC

3.6. To ensure a ductile flexural failure mode and to avoid brittle shear failures, individual column shear capacities were compared with overstrength shear capacities derived from a flexural hinge mechanism at the top and/or bottom of column. Demand-Capacity ratios for bent columns were less than 0.1 for both the longitudinal and transverse directions. All cases are better than the maximum demand-capacity ratio of 1.0. The shear D/C ratios for bent columns are presented in Table 5A and Table 5B in Appendix A3 for longitudinal and transverse directions, respectively.

Bent Cap Strength

The provided bent cap shear reinforcement does not satisfy the LFD minimum reinforcement requirements but both the flexural and shear strengths were found to be adequate to resist the load demands due to column over strength requirements specified in Caltrans SDC 4.3. The flexural and shear demand-capacity ratio were 0.58 and 0.48, respectively. The expected nominal moment capacity for bent cap is based on the expected concrete and steel strengths when either the concrete strain reaches 0.003 or the reinforcing steel reaches the reduced ultimate tensile strain as derived from the steel stress strain model in accordance with Caltrans SDC 3.4.

Abutment and Bent Cap Seat Width

Since the abutments are rigidly connected to the adjacent bridge spans, there is no need to check seat width. However, seats have been provided at each bent to support the center span of the bridge. Currently, the bridge structure is fastened to the cap by use of #8 dowels. These dowels do not have adequate capacity to resist seismic shear demands and will likely shear off during a major seismic event. Despite failure of these pins, the 1’-9”+ available width should be adequate to resist the maximum longitudinal displacement of the superstructure which is approximately 6.5”. However, it is recommended that the seat width be upgraded to meet the current minimum requirement of 2’-6” specified in Caltrans SDC 7.8.3. In addition, transverse shear keys should be provided to limit differential transverse movement of the middle span.

Abutment and Bent Foundation Capacities

The bent foundations were checked for pile failure. The bent footings were found to have adequate capacity under seismic loading based on this analysis.

Joint Degradation Effects

Per MTD 20-4, joint shear is not typically a collapse mechanism and retrofit is not usually required. However, for bridges designed prior to 1971 which typically have minimal steel in the joints, the joints will likely degrade to the point where it loses its moment resisting capacity at

Basis of Design 12 small deformations. Following Joint Shear Modeling Guidance for Existing Structures provided in BDA 14-4, the joint degradation effects are evaluated. The joints were found to be at risk of losing capacity during a major earthquake. A separate model, accounting for the effects of joint degradation, was used to determine that the maximum demand-capacity ratios would only rise from approximately 0.10 to about 0.30 showing that collapse is not an issue.

XII. Conclusions and Retrofit/Repair Recommendations

The longitudinal and transverse seismic assessment and retrofit evaluation is performed, and following vulnerabilities are identified.

1. Insufficient capacity of bent cap dowels.

2. Insufficient seat width at bent cap.

In order to address these seismic deficiencies the following retrofit measures are recommended:

1. Increase the pier seat width: This work will consist of increasing the seat width by at least 1 ft at Bent 2 and Bent 3. Reinforcing dowels will be drilled into the face of the existing bent cap face. Additional bar reinforcing will be placed within the seat extension prior to concrete placement.

2. Install transverse shear keys at the bents: This work will consist of forming 1 ft wide shear keys at Bent 2 and Bent 3. A total of 2 shear keys are required at each bent.

Reinforcing dowels will be drilled into the existing concrete surface. Additional bar reinforcing will be placed within the shear key prior to concrete placement.

Prior studies and inspections noted a number of deficiencies and recommended maintenance repairs. The damage and deficiencies noted in these previous studies have been evaluated and the following general repairs and upgrades are recommended and noted on the plans:

1. Patch and repair spalled concrete: Unsound concrete will be removed to expose sound hard concrete substrate. Existing reinforcement will be protected in place and cleaned for rust. A Portland Cement Concrete patch will be placed to match the original concrete surface. Patch and repair is required at Bent 3 and at one location along the face of girder at Span 2.

2. Replace existing barrier with new a Type 732 barrier: The existing curb and railing will be removed along with adjacent asphalt concrete surfacing. Reinforcing dowels will be drilled into the bridge deck. At Span 2 a concrete overlay will be placed. Additional bar reinforcing will be placed within the barrier prior to concrete placement.

3. Replace approach Metal Beam Guard Rail

4. Replace the corroded utility hangers

Basis of Design 13

XIII. Construction Requirements

Construction requirements are included in the Intermediate Design (35%) submittal.

XIV. Cost Estimate

A cost estimate is included in Appendix A4.

Basis of Design A1-1

BASIS OF DESIGN

DESIGN OF REPAIRS FOR THE UPPER EL RANCHO ROAD BRIDGE

(VAFB FAC # 1910)

APPENDIX A1

Basis of Design A1-2

Photo 1: West Elevation

Photo #2: East Elevation

Basis of Design A1-3

Photo #3: View Facing West

Photo #4: Bent 2 (Facing East)

Basis of Design A1-4

Photo #5: Bent 3 (Facing East)

Photo #5: Span 3 (Facing East)

Basis of Design A2-1

BASIS OF DESIGN

DESIGN OF REPAIRS FOR THE UPPER EL RANCHO ROAD BRIDGE

(VAFB FAC # 1910)

APPENDIX A2

17800 Newhope Street, Suite B, Fountain Valley, California 92708 Tel: (714) 751-3826 Fax: (714) 751-3928

Earth Mechanics, Inc.

Geotechnical & Earthquake Engineering

TECHNICAL MEMORANDUM

DATE: December 13, 2012 EMI PROJECT NO: 12-140

TO: Kosal Krishnan / AECOM

FROM: Arul Arulmoli / Earth Mechanics, Inc. (EMI) Ranjan Gunaranjan / EMI

SUBJECT: Design of Repair for Upper El Rancho Road Bridge, Geotechnical Memorandum for Design ARS Curve and Pile Load Capacity Recommendations

Earth Mechanics, Inc. (EMI) prepared this memorandum to document preliminary geotechnical input such as design ARS recommendations, results of axial pile load capacity estimates, and point of fixity depth estimates to assist AECOM for the 35% design efforts of repair for Upper El Rancho Road Bridge.

Existing Bridge Information

As a part of the preparation of this memorandum, the Structural Analysis Report (Bengal, 2007) and the Routine Bridge Inspection Report (Bengal, 2011) prepared for the Upper El Rancho Road Bridge by Bengal Engineering, Inc. (Bengal) were reviewed. Based on our review, the subject bridge and the approach roadways may be constructed on an ancient landslide or landslide complex. However, no signs of any current global slope instability were observed during their inspection. The available reports indicate that the embankment fill slopes appear to be composed of fine-grained sand and silty sands.

The existing Upper El Rancho Road Bridge, located at Vandenberg Air Force Base, California (approximate latitude of 34 50′ 03" and approximate longitude of 120 34′ 02"), was constructed in 1961. It is an approximately 157 feet long and 30 feet wide three-span concrete girder bridge supported on 28-inch diameter drilled cast-in-place (CIP) columns with enlarged “bell” of 56-inch diameter near the tip. Based on the 1961 as-built plans provided by AECOM, each pier is supported on six CIP columns, while each abutment is supported on five CIP columns. The CIP columns at both piers are embedded approximately 15 feet into the ground, while the CIP columns at northern and southern abutments are embedded approximately 41 feet and 36 feet, respectively, into the ground. Copies of the as-built plans are provided in Attachment 1.

Existing Soil Information

The as-Built Log-of-Test-Borings (LOTB) sheets for the original Upper El Rancho Road Bridge construction was reviewed as a part of the preparation of this memorandum. Copies of the LOTB sheets are provided in Attachment 1.

Design of Repair for Upper El Rancho Road Bridge Project Preliminary Geotechnical Input for 35% Design Efforts

December 13, 2012

The as-built LOTB sheets for the original bridge construction show that a total of seven power auger borings were conducted in February 1961. The top-of-hole elevations vary from about +252 to +265 feet, and each boring was advanced to 50 feet deep. Based on the borings, stratigraphy at the bridge site area generally consists of 30 to 34 feet thick medium dense to very dense sandy materials overlying stiff to very stiff fine-grained materials down to the depth explored. The as-built LOTB sheets show that groundwater was encountered at about depths between 31 feet and 47 feet below grade.

Seismic Design Criteria

To develop the ARS curves using Caltrans ARS online v2.0.4 (Caltrans, 2012) in accordance with the 2010 Seismic Design Criteria (SDC) (Caltrans, 2010) and Geotechnical Services Design Manual (Caltrans, 2009c) procedures, we considered the following response spectra. The resulting ARS curve is the envelop of all the following spectra:

Deterministic Criteria based on late-Quaternary faults in the 2007 fault database (Shantz and Merriam, 2009 and Caltrans, 2009a and 2009b).

Probabilistic Criteria based on 5% in 50 years probability of exceedance ground motion.

Minimum Deterministic Spectrum based on a Mw = 6.5 strike-slip event occurring at a distance of 7.5 miles (12 km) from the site.

The probabilistic response spectrum is based on data from the 2008 United States Geological Survey (USGS, 2008a) National Seismic Hazard Map for the 5% in 50 years probability of exceedance (975-year return period) ground motion.

Based on the subsurface profile interpreted from the as-built LOTB sheets, small-strain shear wave velocities (Vs30) of 600 and 902 feet per seconds (ft/sec) were assumed for the subsurface materials encountered at the bridge site.

ARS curves were developed for the above Vs30 values. The recommended design ARS curve is the envelop of both ARS curves, which is presented in Figure 1 together with the digitized coordinates. As shown in Figure 1, a peak ground acceleration (PGA) of 0.533 g is obtained from the design ARS curve. Table 1 summarizes the key site parameters for the Caltrans ARS online v2.0.4 (Caltrans, 2012).

TABLE 1. SUMMARY OF SITE CHARACTERISTICS

Site Characteristics

Site Coordinates Latitude = 34.8342 degrees Longitude = -120.5672 degrees

Assumed Vs30 600 ft/sec (183 m/sec) and 902 ft/sec (275 m/sec)

Axial Capacity of Existing Pile

Based on the soil data collected from the as-built LOTB sheets, we estimated preliminary axial pile load capacities for the existing pile foundations using the computer program SHAFT Version 6.0 (Ensoft, 2007) and following the guidelines given in NAVFAC Design Manual (NVAFAC, 1986). Table 2 summarizes the ultimate and allowable load capacities for the piles.

TABLE 2. ESTIMATED PRELIMINARY LOAD CAPACITIES FOR EXISTING PILES

Support Ultimate Load Capacity in Compression for Extreme

Limit Condition (kips)

Ultimate Load Capacity in Tension for

Extreme Limit Condition (kips)

Allowable Load Capacity in

Compression for Service Condition (kips)

Abutments 300 150 100

Piers 150 10 50

Lateral Capacity of Existing Piles

Lateral pile capacity of a single 28-inch diameter drilled CIP pile was evaluated for a fixed-head condition using the computer program LPILE (Ensoft, 2010). The internally generated p-y curves for sandy soils were estimated using the API criteria (API, 2000) whereas the p-y curves for fine-grained soils were estimated using the method proposed by Matlock (Matlock, 1970).

An 80% cracked flexural stiffness value was used in the analyses.

For pile head displacements vary from 0.5 to 8 inches, point of fixity values were generated for structural designers to use in their preliminary design stages. Based on our analyses, the preliminary estimated depths to points of fixity below grade for abutment piles ranged between

5.4 and 8.3 pile diameters for a fixed-head condition.

Since the pier piles are embedded only 15 feet (i.e., 6.4 pile diameters) into the ground, no fixity is expected at the pile tip.

Closure

We appreciate the opportunity to work with you on this project. If you have any questions, please do not hesitate to call us.

Sincerely, EARTH MECHANICS, INC.

(Ranjan) G. J. Gunaranjan, GE 2970 Senior Staff Engineer

(Arul) K. Arulmoli, GE 2090 Project Manager

References

American Petroleum Institute (API), 2000, “Recommended Practice and Planning, Designing, and Constructing Fixed Offshore Platforms - Working Stress Design”, API RP2A, Washington, D.C., December.

Bengal Engineering, Inc. (Bengal), 2011, “Routine Bridge Inspection Report of Upper El Rancho

Road Bridge (VAFB-FAC # 1910), Vandenberg Air Force Base, California”, Project No.

XUMU 10-1314E, Contract No. FA4610- 07-D-0003, January 7.

Bengal, 2007, “Structural Analysis Report of Upper El Rancho Road Bridge, FAC # 1910, Vandenberg Air Force Base, California”, Project No. XUMU 11-1042E, Contract No.

FA4610- 07-D-0003, November 6.

California Department of Transportation (Caltrans), 2012, Caltrans ARS Online Version 2.0.4, http://dap3.dot.ca.gov/shake_stable/

Caltrans, 2010, Seismic Design Criteria, Version 1.6, November.

Caltrans, 2009a, 2007 Fault Database, http://dap3.dot.ca.gov/shake_stable/technical.php

Caltrans, 2009b, Fault Errata Report, http://dap3.dot.ca.gov/shake_stable/technical.php

Caltrans, 2009c, Geotechnical Services Design Manual, Division of Engineering Services, Geotechnical Services, Version 1.0, August.

Ensoft, 2010. LPILE Plus Version 6.0, A Program for Analyzing Stress and Deformation of a Pile or Drilled Shaft under Lateral Loading, Austin, Texas.

Ensoft, 2007. SHAFT Version 6.0, A Program for the Study of Drilled Shafts under Axial

Loading, Austin, Texas.

Matlock, H., 1970, “Correlations for Design of Laterally Load Piles in Soft Clay”, Proceedings, 1970 Offshore Technology Conference, Paper No. 1204.

Shantz, T., Merriam, M., 2009, Development of the Caltrans Deterministic PGA Map and

Caltrans ARS Online, California Department of Transportation, Sacramento, CA.

U.S. Geological Survey (USGS), 2008a, Documentation for the 2008 Update of the United

States National Seismic Hazard Maps: U.S. Geological Survey Open-File Report 2008- 1128, 61p.

U.S. Geological Survey (USGS), 2008b, USGS Probabilistic Seismic Hazard Analysis, http://eqint.cr.usgs.gov/deaggint/2008/index.php.

Figure

Figure 1 – Recommended Design ARS Curve

Attachment

Attachment 1 – Copies of 1961 As-Built Plans and Log of Test Borings (LOTB) Sheets for Upper El Rancho Road Bridge

Latitude = 34.8342 Longitude = -120.5672

Damping Ratio = 5%

Period (sec)

Design Acc. (g)

0.010 0.533

0.100 0.746

0.200 0.953

0.300 1.036

0.500 1.048

1.000 0.908

2.000 0.610

3.000 0.382

4.000 0.260

5.000 0.195

Date: 12/13/12

Upper El Rancho Road Bridge Design ARS Curves Using Caltrans Online v2.0.4

Project: 12-140 Figure 1

Spectral Coordinates

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

S p e ct ra l A cc e le ra tio n g

Period (sec) o o

Basis of Design A3-1

BASIS OF DESIGN

DESIGN OF REPAIRS FOR THE UPPER EL RANCHO ROAD BRIDGE

(VAFB FAC # 1910)

APPENDIX A3

Basis of Design A3-2

Basis of Design A3-3

Basis of Design A3-4

Basis of Design A3-5

Basis of Design A3-6

Basis of Design A3-7

Basis of Design A3-8

Basis of Design A3-9

Basis of Design A3-10

Basis of Design A4-1

BASIS OF DESIGN

DESIGN OF REPAIRS FOR THE UPPER EL RANCHO ROAD BRIDGE

(VAFB FAC # 1910)

APPENDIX A4

Basis of Design A5-1

BASIS OF DESIGN

DESIGN OF REPAIRS FOR THE UPPER EL RANCHO ROAD BRIDGE

(VAFB FAC # 1910)

APPENDIX A5

Basis of Design A5-2

Table of Contents for Drawings

The following list provides the table of contents for the project plans:

Title Sheet Site Plan General Plan Structure Notes and Index to Plans Concrete Repair Plan Details Barrier Rail Replacement Details Bent Details No. 1 Bent Details No. 2 Waterline Hanger Details Miscellaneous Details

DATE DESCRIPTION OF REVISION SYMBOL

PR

O

JE

C

T

D

RA

W

IN

G

DATE

O F

SCALE

DRAWING TITLE

PROJECT TITLEDRAWN

REVIEWED

DESIGNED

FOR OFFICIAL USE ONLY -- INFORMATION SAFEGUARDING IS REQUIRED

The information contained on this drawing shall remain under the control of the originating requester or agency or ts successor in function at all times. Information safeguarding is the responsibility of the individual/agency/company requesting the data and taking original possession of this drawing. Release/disclosure of data to any party beyond the original request and intended use is prohibited. No public publication of the data by any means or analyses thereof is authorized. Upon completion of the use of the data contained on this drawing, the drawing must be returned or destroyed.

Direct any questions to the Engineering Support Element, 30 CES/CECB, at 805-606-4716.

Information safeguarding requirements are per AFMAN37-104, AFI 33-332, DOD Reg 5400.11, and Executive Order 12958 (when applicable).

DO NOT DUPLICATE THIS DRAWING -- OR THE DATA CONTAINED ON IT

Basis of Design A6-1

BASIS OF DESIGN

DESIGN OF REPAIRS FOR THE UPPER EL RANCHO ROAD BRIDGE

(VAFB FAC # 1910)

APPENDIX A6

Basis of Design A6-2

Support Information and Client Direction

There is no documentation of interviews and discussions to be included at this time.

Basis of Design A7-1

BASIS OF DESIGN

DESIGN OF REPAIRS FOR THE UPPER EL RANCHO ROAD BRIDGE

(VAFB FAC # 1910)

APPENDIX A7

Basis of Design A7-2

List of Recycled Materials

Not Applicable.

Basis of Design A8-1

BASIS OF DESIGN

DESIGN OF REPAIRS FOR THE UPPER EL RANCHO ROAD BRIDGE

(VAFB FAC # 1910)

APPENDIX A8

Basis of Design A8-2

Inventory and Load Study

Not Applicable. Not in scope of work.

Basis of Design A9-1

BASIS OF DESIGN

DESIGN OF REPAIRS FOR THE UPPER EL RANCHO ROAD BRIDGE

(VAFB FAC # 1910)

APPENDIX A9

Basis of Design A9-2

Technical Field Investigations

A separate Investigation Report will be submitted at a later date.

Basis of Design A10-1

BASIS OF DESIGN

DESIGN OF REPAIRS FOR THE UPPER EL RANCHO ROAD BRIDGE

(VAFB FAC # 1910)

APPENDIX A10

Basis of Design A11-1

BASIS OF DESIGN

DESIGN OF REPAIRS FOR THE UPPER EL RANCHO ROAD BRIDGE

(VAFB FAC # 1910)

APPENDIX A11