ARBORVIEW PROJECT Structural Design Criteria For … · 3 DESIGN SCOPE This outlines the criteria to be used for the structural engineering design of the post-tensioned ground-supported

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STRUCTURAL ENGINEERING CONSULTANTS

ARBORVIEW PROJECT

Structural Design Criteria For Post-Tensioned Ground-Supported Slabs

Prepared by

The Structural Engineering Consultants (SECI)

27200 Tourney Rd, Suite 390 Valencia, CA 91355

For

FIELDSTONE COMMUNITIES, INC

Santa Clarita, CA 91350

calc_legend_plaza

TN213_SOG_design_criteria_12 020606

LIST OF CONTENTS

1. DESIGN SCOPE 2. DESIGN CONSIDERATIONS 3. CALCULATION RESULTS

• Plan 1A • Plan 2A • Plan 2C • Plan 3A • Plan 3B

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DESIGN SCOPE

This outlines the criteria to be used for the structural engineering design of the post-tensioned ground-supported slabs of the subject matter project.

The structural design for the remainder members of the concrete frame is reported in a separate structural calculation package. Work reported separately includes both the gravity and lateral aspects of the design. The calculations reported herein are based on the set of drawings listed in the appendix of this report. The parameters used for the design of the slabs are based on preliminary values provided in the following: Letter from: Pacific Soils Engineering, Inc., located at 10553 Progress Way, Cypress, CA 90630, Tel (714) 220 0770, Fax: (714) 220 9599, signed by Paul Ernst, RGE and dated, January 30, 2006. Addressed to: Fieldstone Communities, Inc., located at 21080 Center Pointe Parkway, Suite 102, Santa Clarita, CA 91350.

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1. DESIGN CONSIDERATIONS 1.1 Structural System The structural system of the foundation is a mat slab of uniform thickness with down turned perimeter beams resting on soil. The slab is post-tensioned in both directions with straight tendons placed at mid-depth of the slab. A moisture and vapor retarding system is recommended by the soil engineer to be placed below the slab.1 This design criteria is used for several configurations of the slab foundations of the subject matter tract. Unless specified otherwise, the slab thickness is 9 inch. The perimeter beams are 24 inch deep and 12 inch wide.

1.2 Applicable Codes The design is based on UBC 1997. Where this code is mute, PTI’s recommendations given in “Design of Post-Tensioned Slabs-on-Ground” is used. Both of the above documents are simplifications derived from a more rigorous finite element plate analysis. As such, they do not fully cover the range of loading and configurations of the subject project. Where design recommendations are lacking, ADAPT’s SOG Manual on “Post-Tensioned Foundation Slabs on Expansive or Compressible Soil” is used. Using the code design criteria, the analysis is based on a finite element program that accounts for the following:

• Authentic representation of geometry of the slab, beams, depressions, steps, thickenings, and material properties

• Modeling of tendons, where they occur (correct profile, eccentricity, stress losses)

• Ability to apply specified edge lift as required by code and allow for separation of slab from soil

• Ability to apply centre lift as required by code • Reduction of the local stresses to the representative values for

code • Use of a shell element to account for both the bending and in-plane

response of the slab

1.3 Structural Documents The calculations and structural drawings conclude with:

(i) The detailed layout of tendons in the foundation slab, showing the location, profile and height of each;

1 10-mil plastic membrane, such as Visqueen.

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(ii) The non-prestressed reinforcement over and above the post-tensioning tendons, at all locations on the slab;

(iii) Construction notes and details.

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1.4 Material Properties

1.4.1 Concrete: Weight = 150 pcf Cylinder Strength at 28 days for slabs = 4000 psi Modulus of Elasticity (instantaneous) = 3605 ksi

Modulus of Elasticity (creep) = 1800 ksi Creep Coefficient = 2

1.4.2 Post-Tensioning: MATERIAL Low Relaxation

Strand Diameter = 0.50 in nominal Strand Area = 0.153 in2 Modulus of Elasticity = 28000 ksi Guaranteed Ultimate Strength (fpu) = 270 ksi Average Effective Stress (fse) = 175 ksi

SYSTEM System unbonded Angular Coefficient of Friction (µ) = 0.07 Wobble Coefficient of Friction (K) = 0.001 rad/ft Anchor Set (Wedge Draw-in) = 0.25 inch

1.4.3 Non-prestressed Reinforcement:

Yield Strength = 60 ksi Modulus of Elasticity = 30000 ksi

1.4.4 Friction Between Foundation Slab and Soil: Friction Coefficient = 0.40

1.4.4 Design Loading A base load common to all foundation slabs is used. In addition to the base load, each slab is subjected to loads that reflect the construction of the respective superstructure. BASE LOAD DEAD LOAD

Self weight = based on volume Partitions = 20.0 psf Total = 20.0 psf + self weight

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LIVE LOAD

Uniformly Distributed = 40.0 psf

BUILDING SPECIFIC LOADS These consist of dead, live, and seismic loads. They are shown on the design plans prepared for each foundation.

2. LOAD CASES; LOAD COMBINATIONS AND STRESSES Three series of checks are performed:

• Service condition • Initial (transfer of prestressing) condition • Strength condition

The foundation is sized based on the in-service condition. It is checked against other load cases, and reinforced if necessary. The following describes the conditions and criteria used for each.

2.2 Serviceability Load combinations (i) Average Precompression: The post-tensioning design targets an

average precompression over the entire cross-sectional area of the foundation not less than 75 psi after all losses. In most instances a precompression around 100 psi is used.

(ii) Load Cases and Allowable Stresses

The load cases for in-service condition are “edge lift” and “center lift.” The design parameters for these two cases are specified by the soil engineer and given below:

• Center lift o ym = 1.5 in. o em = 5.0 ft

• Edge lift

o ym = 0.40 in. o em = 3.5 ft

For each of the preceding load cases, representative concrete stresses are calculated and compared with the allowable values for code compliance. The allowable values are:

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Allowable Tensile Stress:

ft = 6 * f’c0.5

= 6 * 4000 0.5 = 379 psi

Allowable Compressive Stress:

fc = 0.45 * f’c = 0.45 * 4000 = 1800 psi

Allowable Shear Stress

vc = 1.7 * f’c0.5 + 0.2fp = 1.7 * 4000 0.5 + 0.2 * 100 = 127 psi where fp is the average precompression

Soil Bearing Pressure

• Bearing pressure under the slab: 1000 psf • Bearing pressure under beam stem (18 “ or more below

grade) = 1500 psf

Allowable Deflection Maximum differential displacement (relative deflection) of the

top of the slab 1/300 over any length of slab

(iii) Load Combinations For Serviceability Check

“Total” in-service load combination (stress check): U = 1.00DL + 1.00LL + 1.00Prestressing

2.3 Initial Condition (Transfer of Prestressing Force)

Load combination for stress check at transfer of prestressing: U = 1.15 * Prestressing

Allowable Tensile Stress:

ft = 3 * f’c0.5

= 3 * 4000 0.5 = 189 psi

Allowable Compressive Stress:

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fc = 0.60 * f’c

= 0.60 * 4000 = 2400 psi

2.4 Strength Load Combinations The strength load combination is used to check the adequacy of the foundation slab under seismic forces .The strength requirement for each location is established using the following factored load combinations:

U = 1.20DL + 1.00LL + 1.00Secondary + 1.00E

U = 0.90DL + 1.00Secondary + 1.00E

Where “secondary” consists of the hyperstatic moments, shears and reactions due to post-tensioning.

PLAN 1A

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Plan_1_CL_3.adm

Post-Tensioned Slab-On-GroundArborview

RMM

ADAPT

Plan Geometry

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Plan_1_CL_3.adm

Post_Tensioned Slab_On_GroundArborview

RMM

ADAPT

Member Dimensions (in)

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Plan_1_CL_3.adm


RMM

ADAPT

Member Identifications

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ArborviewRMM

ADAPT

Plan Geometry

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Plan_1_CL_3.adm


RMM

ADAPT

Dead Load Plan(ksf, k/ft, kip)

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Plan_1_CL_3.adm


RMM

ADAPT

Live Load Plan (ksf,k/ft,k)

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Plan_1_EQ_Loads.adm


ADAPT

RMM

Loading Plan Seismic Load (kip)

Support Line 1

Support Line 2

Support Line 3

Support Line 4

Support Line 5

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Plan_1_CL_2.adm


ADAPT

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REPORT_Design Strips X-direction

Support Line 6

Support Line 7

Support Line 8

Support Line 9

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Plan_1_CL_2.adm


ADAPT

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REPORT_Design Strips Y-direction

Support Line 1

Support Line 2

Support Line 3

Support Line 4

Support Line 5

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Plan_1_CL_2.adm


ADAPT

RMM

REPORT_Support Lines X-direction

Support Line 6

Support Line 7

Support Line 8

Support Line 9

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Plan_1_CL_2.adm


ADAPT

RMM

REPORT_Support Lines Y-direction

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Plan_1_CL_3.adm


RMM

ADAPT

Tendon Plan

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ArborviewRMM

ADAPT

Tendon 3D View

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Plan_1_CL_2.adm


ADAPT

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Mesh

• CENTER LIFT DESIGN

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Plan_1_CL_2.adv

Post_Tensioned Slab_On_GroundZ-Translation - Service

Unit :

Deformation

Deflection Profile

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Plan_1_CL_2.adv

Post-Tensioned Slab_On_GroundStress - Service

Unit :

Spring Forces

Soil Pressure

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Plan_1_CL_2.adm


ADAPT

RMM

Stress Check in X-Direction

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Plan_1_CL_2.adm


ADAPT

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Stress Check in Y-Direction

• EDGE LIFT DESIGN

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Plan_1_EL_2.adv Z-Translation - Service Unit :

Deformation

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Plan_1_EL_2.adv

Post-Tensioned Slab_On_GroundStress - Service

Unit :

Spring Forces

Soil Pressure

Support Line 1

Support Line 2

Support Line 3

Support Line 4

Support Line 5

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Plan_1_EL_2.adm

Post-Tensioned Slab_On_GroundArborview

ADAPT

RMM

REPORT_Stress Check in X-direction

Support Line 6

Support Line 7

Support Line 8

Support Line 9

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Plan_1_EL_2.adm

Post-Tensioned Slab_On_GroundArborview

ADAPT

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REPORT_Stress Check in Y-direction