OSD Seismic Retrofit Report~1.pdf

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Seismic Evalua� on Report For:

OAKRIDGE ELEMENTARY SCHOOL

48119 E 1st St, Oakridge, OR 97463

Oakridge School District

Prepared By:

ZCS Engineering & Architecture

Ma! hew R. Smith, PE, SE, Principal

524 Main Street, Suite 2, Oregon City, OR 97045

503.659.2205 | Ma! S@zcsea.com

Oakridge School District December 2023

Oakridge Elementary School Seismic Evaluation Project No: P-2810-22

Project Summary Information

Building

Part

Part Name

Included in

Retrofit

Year

Built

Type***

Nonstructural Retrofits Included in Scope Y/N***

Previous Seismic

Retrofit Y/N***

(Year if Yes)

A Main Building N 1948

B Gymnasium Y 1954 W2, C2a Y N

*** Entries required ONLY for building parts included in proposed seismic retrofit

Nonstructural deficiencies posing life safety risk MUST be included in the scope of work and budget.

Seismic fragility inputs for existing buildings with previous seismic retrofits MUST be adjusted to reflect previous seismic retrofit measures completed for a building part.

Total Retrofit Cost $2,498,920

Retrofit Square Feet 18,600

Retrofit Cost per Square Foot

$134.35

Is the campus within a tsunami, FEMA flood zone, landslide/slope instability, liquefaction potential or other high hazard area? If so, provide documentation.

Yes, per HazVu.

Hazard ruled out per Geotech report.

Engineering Report Checklist

☒ Engineering Report Cover Page

☒ Project Summary Page Page 1

☒ Building Parts Identification Page 4

☒ Statement of the Performance Objective Page 6

Summary of Deficiencies

☒ Structural Seismic Deficiencies Page 10

☒ Nonstructural Seismic Deficiencies Page 12

Summary of Mitigation/Retrofit

☒ Structural Mitigation/Retrofit Page 10

☒ Nonstructural Mitigation/Retrofit Page 12

Summary Construction Cost Estimate

☒ Direct Cost Page 14

☒ Indirect Soft Cost Page 14

☒ Certification Statement by Engineer Page 15

ASCE 41-17 Tier 1 Checklist

☒ Basic Configuration Checklist Appendix B

☒ Building System Structural Checklist Appendix B

☒ Nonstructural Checklist Appendix B

☒ Retrofit Drawings & Sketches Appendix C

☒ DOGAMI or Geotechnical Report Appendix D

☒ Itemized Construction Cost Estimate Appendix E

☒ Rapid Visual Screening Appendix F

1.0 Project Introduction

Oakridge School District is located in Oakridge, Oregon in Lane County. The District operates two schools located within the community including the property of interest, Oakridge Elementary School. The District has retained ZCS Engineering and Architecture (ZCS) to perform a seismic evaluation of Oakridge Elementary School that provides the District with an objective, comprehensive analysis of the condition of the building’s seismic resisting systems. The purpose of the evaluation is to determine the seismic lateral resisting system deficiencies when compared to buildings designed using modern building codes. This evaluation was performed in accordance with the American Society of Civil Engineers “Seismic Rehabilitation of Existing Buildings ASCE/SEI 41-17”.

SEISMIC EVALUATION SNAPSHOT

Street Address 48119 E 1st Street, Oakridge, OR

Evaluation Standard ASCE 41-17 (Tier 1 Analysis)

Target Building Performance Level Immediate Occupancy – BSE-1E; Life Safety –

BSE-2E

Target Non-Structural Performance Level Position Retention – BSE-1E; Hazards Reduced

– BSE-2E

ASCE 41 Building Type W2, C2a

Site Soil Classification C

Seismic Zone Hazard Level Moderately High

Cost Estimate $2,498,920

Construction Year: 1948

Building Name: Classrooms

Not in Scope

Construction Year: 1954 Building Name: Gymnasium

Construction Type: W2, C2a

2.0 Building Description

The elementary gym (Area B) was constructed in 1954 as an addition to the original school building. The roof structure consists of bowstring trusses, glulam beams with straight sheathing and decking over top. The roof is then supported by conventional wood framed walls down to foundation. The gym floor consists of a crawlspace with floor joist supported on strip footings. A second floor occurs between the gym and the original building, the floor is framed with wood floor joist supported by wood stud walls. The structure between the gym and classrooms building is supported by a slab on grade with conventional spread and strip footings.

Photographs of the building parts included in this report are located in Appendix A.

Figure 1

Oakridge Elementary School Seismic Retrofit Key Plan

A

B

B

3.0 Definition of Building Types

After reviewing the facility and the existing drawings we have determined the lateral system is defined as W2. Per ASCE 41-17 the subject structure’s lateral system is defined as:

Wood Frames, Commercial and Industrial W2 – These buildings are commercial or industrial buildings with a floor area of 5,000 ft2 or more. There are few, if any, interior walls. The floor and roof framing consists of wood or steel trusses, glulam or steel beams, and wood posts or steel columns. The foundation system may consist of a variety of elements. Seismic forces are resisted by wood diaphragms and exterior stud walls sheathed with plywood, oriented strand board, stucco, plaster, or straight or diagonal wood sheathing, or they may be braced with rod bracing. Wall openings for storefronts and garages, where present, are framed by a post-and-beam framing.

Concrete Shear Walls C2 – These buildings have floor and roof framing that consists of cast-in-place concrete slabs, concrete beams, one-way joists, two-way waffle joists, or flat slabs.

Buildings may also have steel beams, columns, and concrete slabs for the gravity framing. Floors are supported on concrete columns or bearing walls. Seismic forces are resisted by cast-in-place concrete shear walls. In older construction, shear walls are lightly reinforced but often extend throughout the building. In more recent construction, shear walls occur in isolated locations, are more heavily reinforced, and have concrete slabs that are stiff relative to the walls. The foundation system may consist of a variety of elements.

C2a (with flexible diaphragms) – These buildings are similar to C2 buildings, except that diaphragms consist of wood sheathing, or have large aspect ratios, and are flexible relative to the walls.

4.0 Seismic Evaluation Methodology

The subject structure was evaluated using information gathered from site observations, available historic construction documents, and interviews with District staff. This information was then utilized to perform a structural evaluation as outlined in the American Society of Civil Engineer’s “Seismic Evaluation and

Retrofit of Existing Buildings – ASCE 41-17” (ASCE 41-17). ASCE 41-17 is referenced as the standard for seismic evaluations of existing buildings by the International Existing Building Code (IEBC) which is referenced by the Oregon Structural Specialty Code (OSSC). Further, ASCE 41-17 is the evaluation tool required by the Seismic Rehabilitation Grant Program for grant applications.

ASCE 41-17 provides several levels of evaluation (Tiers 1-3) depending on the level of evaluation and/or retrofit being performed. The Tier 1 evaluation is a quick checklist selected based on the type of construction and the performance objective of the building and is the baseline tool for preliminary seismic evaluations. In the case of this evaluation, a Tier 1 was performed to identify the likely structural deficiencies requiring retrofit to meet the performance objective stated below.

The OSSC classifies buildings into risk categories based on the type of building and occupancy type. The building’s risk category informs the required performance objective post retrofit. Risk categories I and II cover low risk structures. Risk category III includes school buildings that are not required to be used as emergency shelters and are relatively low occupancy. Risk category IV includes emergency service buildings and school buildings that are required to be designed as emergency shelters (high occupancy spaces). Figure 2, below, identifies the performance objective for each risk category.

The primary objective of the adjusting performance objectives relative to risk category is to ensure that the subject building is capable of performing in the necessary manner following a seismic event. In the case of a risk category III building, the intention is to ensure that the building is adequately stable following an earthquake to provide egress for occupants out of the building. Prior to reoccupation, the building would need evaluated and significant structural damage preventing reoccupation may be present. For risk category IV structures, the intent is that the building can be inspected then immediately reoccupied following a seismic event to function in its intended role as an emergency service building or as a high occupancy space capable of acting as an emergency structure.

In accordance with the table below, section B of this building is categorized as a risk category IV structure and was evaluated to meet the Life Safety structural performance and Hazards Reduced nonstructural performance level for BSE-2E loading and the Immediate Occupancy structural performance and Position Retention nonstructural performance level for BSE-1E loading.

Figure 2

Building Performance Objectives

Source: Table 2-2, ASCE 41-17: American Society of Civil Engineers – Seismic Evaluation and Retrofit of Existing Buildings

5.0 Seismicity

Seismic design is based on site specific parameters that relate to the location of the building relative to faults and the soil that supports the building. The United States Geologic Survey has developed seismic design data that is utilized to perform the calculations specified in ASCE 41-17. The table below summarizes the factors appropriate for computing the seismic lateral loads for the design earthquake specified in ASCE 41-17.

SITE SPECIFIC SEISMICITY

Soil Density Stiff Soil

ASCE 7-16 Soil Classification C

BSE-1E:

Sxs 0.16

Sx1 0.08

BSE-2E:

Sxs 0.47

Sx1 0.30

Soil Condition Amplification Factors (FV, FA) Fv = 2.4 | Fa = 1.6

ASCE 41 Site Seismicity High

Source: SEAOC and OSHPD Seismic Design Maps, https://seismicmaps.org/

6.0 Site Specific Hazards

Site specific hazards were assessed as part of our engineering evaluation. The hazards evaluated in our analysis included liquefaction, slope failure, surface fault rupture, and tsunami potential. These potential hazards were evaluated using ASCE 41-17 guidelines, as well as information provided by the online

Oregon HazVu: Statewide Geohazards Viewer, maintained by the Department of Geology and Mineral

Industries (DOGAMI). Tsunami risk was evaluated using the ASCE Tsunami Hazard Tool. Results from the

HazVu analysis are included in Appendix D along with a the geotechnical report. Unless noted below, the hazards listed above are not present at the site.

Liquefaction

This project is located within a liquefaction hazard area as identified by the DOGAMI Oregon HazVu. To ensure that an acceptable level of due diligence was performed during the application phase of the project a geotechnical report from an adjacent project was obtained to confirm whether or not a hazard is present. Per the geotechnical report, attached in Appendix D, liquefaction is considered a low risk for the site and no mitigation is required.

7.0 Deficiencies and Repairs

The table below summarizes both the structural and nonstructural deficiencies noted in the Tier 1 evaluation and states both the proposed retrofit methodology and the plan key note that corresponds to the scope items in the preliminary plans and the cost estimate. See Appendix B for complete Tier 1 check sheets. Drawings illustrating the proposed retrofit measures are attached in Appendix C.

Tier 1 Deficiency Description

Deficiency Statement Repair Statement Plan Key Note

IO BASIC CHECKLIST

LOAD PATH The structure does not contain a complete, well-defined load path, including structural elements and connections, that serves to transfer the inertial forces associated with the mass of all elements of the building to the foundation.

Provide a complete, well-defined load path by installing new elements and connections as needed to transfer inertial forces from all elements of the building to the foundation.

S1

ADJACENT

BUILDINGS

The clear distance between the building being evaluated and any adjacent building is less than 0.5% of the height of the shorter building in low seismicity, 1.0% in moderate seismicity, and 3.0% in high seismicity.

Provide seismic joint to separate buildings outside of scope. Provide all new gravity framing and lateral resisting elements as necessary.

S2

W2: IO CHECKLIST

SHEAR STRESS

CHECK

The shear stress in the shear walls, calculated using the Quick Check procedure of Section 4.4.3.3, is higher than the following values:

Structural panel sheathing 1,000 lb/ft Diagonal sheathing 700 lb/ft Straight sheathing 100 lb/ft All other conditions 100 lb/ft

Install new plywood shear walls to ensure adequate shear capacity.

S3

WALLS

CONNECTED

THROUGH

FLOORS

Shear walls do not have an interconnection between stories to transfer overturning and shear forces through the floor.

Install new hardware required for transfer of in-plane shear forces from one floor to the floor below.

S4

HOLD-DOWN

ANCHORS

Not all shear walls have hold-down anchors attached to the end studs constructed in accordance with acceptable construction practices.

Install new hold-down hardware.

S5

WOOD POSTS There is not a positive connection of wood posts to the foundation.

Install hardware at wood posts to ensure connection to the foundation.

S6

WOOD SILLS All wood sills are not bolted to the foundation.

Provide new anchor bolts from wood sills to the foundation.

S7

ROOF CHORD

CONTINUITY

Chord elements are discontinuous. Install new drag elements at discontinuous chords.

S8

STRAIGHT

SHEATHING

Not all straight-sheathed diaphragms have aspect ratios less than 1-to-1 in the direction being considered.

Install new plywood diaphragm sheathing.

S9

SPANS Not all wood diaphragms with spans greater than 12 ft consist of wood structural panels or diagonal sheathing.

Install new plywood diaphragm sheathing.

S10

WOOD SILL

BOLTS

Sill bolts are not spaced at 4ft or less with acceptable edge and end distance provided for wood and concrete.

Provide new anchor bolts from wood sills to the foundation.

S11

C2: IO CHECKLIST

WALL

ANCHORAGE AT

FLEXIBLE

DIAPHRAGMS

Exterior concrete or masonry walls that are dependent on flexible diaphragms for lateral support are not anchored for out-of-plane forces at each diaphragm level with steel anchors, reinforcing dowels, or straps that are developed into the diaphragm. Connections have strength to resist the connection force calculated in the Quick Check procedure of Section 4.4.3.7.

Install new out-of-plane anchorage.

S12

TRANSFER TO

SHEAR WALLS

Diaphragms are not connected for transfer of loads to the shear walls, or the connections are not able to develop the lesser of the shear strength of the walls or diaphragms.

Install new hardware for transfer of seismic forces from diaphragm to shear walls.

S13

CROSS TIES There are not continuous cross ties between diaphragm chords.

Provide new continuous cross ties between diaphragm chords.

S14

VERTICAL SEISMIC COMPONENTS

HEAVY TIMBER

TRUSSES

The existing trusses have been evaluated for gravity loading per section

7.2.2 of ASCE 41-17 equation 7-1

QG =1.1( QD+QL+QS). It has been determined that the demands on the trusses exceed 80% of the expected

Retrofit and strengthen timber trusses to support code required seismic vertical loading.

S15 capacity. Therefore, Vertical seismic effects per section 7.2.5.2 of ASCE 41- 17 have been included in the evaluation. It has been determined, when vertical seismic effects are included in the load combination per equation 7-34, Qud = Qg + Qe the trusses require strengthening.

NONSTRUCTURAL CHECKLIST

SHUTOFF

VALVES

Piping containing hazardous material, including natural gas, does not have shut off valves or other devices to limit spills or leaks.

Install shut off valves for piping containing hazardous material, including natural gas. N1

FLEXIBLE

COUPLINGS

Hazardous material ductwork and piping, including natural gas piping, do not have flexible couplings.

Install flexible couplings for ductwork and piping containing hazardous material, including natural gas piping. N2

TIES Masonry veneer is not connected to the backup with corrosion-resistant ties.

There is not a minimum of one tie for every 2-2/3 ft.2, or the ties have spacing greater than the following: for Life Safety in Low or Moderate Seismicity, 36 in.; for Life Safety in High Seismicity and for Position Retention in any seismicity, 24 in.

Secure existing masonry veneer with new stitch ties.

N3

TALL NARROW

CONTENTS

Contents more than 6 ft high with a height-to-depth or height-to-width ratio greater than 3-to-1 are not anchored to the structure or to each other.

Anchor contents to the structure.

N4

FALL-PRONE

CONTENTS

Equipment, stored items, or other contents weighing more than 20lb whose center of mass is more than 4 ft above the adjacent floor level are not braced or otherwise restrained.

Brace equipment to structure.

N5

FALL-PRONE

EQUIPMENT

Equipment weighing more than 20 lb whose center of mass is more than 4 ft above the adjacent floor level, and which is not in-line equipment, is not braced.

Brace and anchor equipment weighing more than 20 lb, whose center of mass is more than 4 ft above the adjacent floor level. N6

IN-LINE

EQUIPMENT

Equipment installed in line with a duct or piping system, with an operating weight more than 75 lb, is not supported or laterally braced independent of the duct or piping system.

Independently support and laterally brace equipment with an operating weight more than 75 lb installed in line with a duct or piping system.

N7

TALL NARROW

EQUIPMENT

Equipment more than 6ft high with a height-to-depth or height-to-width ratio greater than 3-to-1 is not anchored to the floor slab or adjacent structural walls.

Anchor equipment more than 6ft high with a height-to-depth or height-to-width ratio greater than 3-to-1 to the floor slab or adjacent structural walls. N8

HEAVY

EQUIPMENT

Floor-supported or platform-supported equipment weighing more than 400lb is not anchored to the structure.

Anchor floor-supported or platform-supported equipment weighing more than 400lb to the structure. N9

FLEXIBLE

COUPLINGS

Fluid and gas piping does not have flexible couplings.

Install flexible couplings for fluid and gas piping. N10

FLUID AND GAS

PIPING

Fluid and gas piping is not anchored or braced to the structure to limit spills or leaks.

Anchor and brace fluid and gas piping to the structure.

N11

In addition to the structural and nonstructural deficiencies noted above, the gravity load resisting system was reviewed to identify obvious insufficient gravity components. Insufficient gravity elements can cause failure during seismic events. These gravity deficiencies are based on visual observations of the existing structural elements. No formal structural analysis was performed during this evaluation of the gravity resisting element.

Based upon ZCS’s previous experience and discussions with site personnel the building contains hazardous materials. These materials will need to be dealt with on a case-by-case basis as they are encountered during the project.

8.0 Preliminary Construction Cost Estimate

The attached engineer’s opinion of probable cost has been developed by ZCS. ZCS has a successful record of completing seismic rehabilitation projects within the State of Oregon. The prices provided in the attached cost estimate have been developed using the extensive list of past projects as a baseline for this project. These prices are based on Oregon BOLI wage rates.

The cost estimate is broken down into multiple line items associated with each major task (general conditions, foundation, structural steel, MEP, etc) associated with the rehabilitation.

Additional line items are included for design associated permit costs, and owner construction management. A complete breakdown of the cost estimate can be found in Appendix E.

DIRECT COST

Construction $1,795,400

Engineering $272,800

Construction Management $61,800

Relocation $25,700

Construction Contingency $343,220

TOTALS AND SUMMARY

Total Cost Estimate $2,498,920

Match Funds $0

Total Amount Requested from SRGP $2,498,920

Total Area 18,600

Cost/Square Foot $134.35

9.0 Conclusion and Certification Statement

The findings described in this report have been limited to the lateral force-resisting structural system and general assessment of the gravity force-resisting elements. Based on our visual observations, we find the structure to be in relatively good condition and generally safe for occupancy. No significant damage to the existing structural system was discovered.

Given the current condition of the structure, the current code section on existing buildings does not mandate that upgrades are required unless the building is scheduled for repairs, alterations, additions, or change in occupancy. To clarify, upgrades outlined in this report are strictly at the discretion of the District.

Please contact our office if you would like to discuss our findings. Please review the attached schematic drawings that can be used to refine a scope and budget.

Certification Statement

ZCS Engineering & Architecture’s professional staff has reviewed the subject building and the deficiencies noted in the Tier 1 evaluation, developed seismic retrofit solutions to rectify the deficiencies, and developed the engineering cost estimate. The project cost estimate was developed by ZCS based on unit costs from our extensive list of past seismic retrofit projects as a baseline. We certify to the best of our knowledge, based on known and readily identifiable existing conditions, that all the seismic deficiencies present in the building are included in the retrofit scope of work and that all the retrofit’s scope of work elements are included in the cost estimate.

Matthew R. Smith, PE, SE

Appendix A:

Figures

Figure 1: SOUTHEAST EXTERIOR ELEVATION

Figure 2: WEST EXTERIOR ELEVAITON

Figure 3: INTERIOR WEST ELEVATION

Figure 4: INTERIOR GYM TRUSSES

Figure 5: INTEIROR WEST ELEVAITON

Figure 6: EXTEIROR NORTH ELEVATION

Appendix B:

Tier 1 Check Sheets

Appendix C:

Preliminary Seismic Retrofit

Drawings

Appendix D:

Geotechnical Information

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Oakridge E.S. Landslide Hazard Map

Landslide Hazard

Red: Band_1

Green: Band_2 Blue: Band_3

August 27, 2018

0.04 0.08

0.02 mi

0.07

0.14 0.04 km

1:3,600

Geotechnical Investigation and

Seismic Hazard Study

Oakridge HS Gym & Auditorium

Seismic Retrofit

Oakridge, Oregon

Prepared for:

Oakridge School District c/o PIVOT Architecture

Eugene, Oregon

October 1, 2020

Foundation Engineering, Inc.

Professional

Geotechnical

Services

Oakridge HS Gym & Auditorium Seismic Retrofit October 1, 2020

Geotechnical Investigation and Seismic Hazard Study 1. Project No.: 2181111-102

Oakridge, Oregon Oakridge School District

GEOTECHNICAL INVESTIGATION AND

SEISMIC HAZARD STUDY

OAKRIDGE HS GYM & AUDITORIUM SEISMIC RETROFIT

OAKRIDGE, OREGON

BACKGROUND

The Oakridge School District (District) plans to complete a seismic retrofit of the high school gymnasium, auditorium, and locker room buildings. The site location is shown on Figure 1A (Appendix A). PIVOT Architecture (PIVOT) is the project architect and ZCS Engineering & Architecture (ZCS) is the structural consultant.

PIVOT, on behalf of the School District, previously retained Foundation Engineering to complete a geotechnical investigation for the project in support of a grant application. The focus of the previous investigation consisted of providing geotechnical design information for a planned addition located near the northwest corner of the high school, and for an addition to the elementary school. The findings from the previous investigation at the high school are summarized in a memorandum dated November 14, 2018. Since then, the project has been rescoped and consists of seismically upgrading the gymnasium, auditorium, and locker room buildings, and eliminating the high school addition. Therefore, additional geotechnical services were requested for the project.

Our scope of work was outlined in a proposal dated September 1, 2020, and addresses a list of items requested by the design team. The scope of work was authorized by signed service agreement dated September 2, 2020.

LOCAL GEOLOGY

Detailed discussions of the local and regional geology, tectonic setting, local faulting, historical seismicity, seismic hazards, and design earthquakes are included in the

Seismic Hazard Study report (Appendix D). References cited in this section are also provided in Appendix D. An abbreviated discussion of the local geology is provided below.

The project site is located within the Cascade Range physiographic province, specifically the Western Cascade Range of Central Oregon (Orr and Orr, 1999).

Oakridge is located at the confluence of the Salmon, Salt, and Hills Creeks which combine into the Middle Fork of the Willamette River. The school site is located in north-central Oakridge near the base of a steep, south-facing slope and ±½ mile to the north of the Middle Fork of the Willamette River.

Local geologic mapping indicates the project site is underlain by glaciogenic outwash deposits underlain by tuffaceous volcaniclastic rocks of the Little Butte Volcanics

(Sherrod, 1991). The outwash deposits include terraces of well-graded to moderately-graded sand and gravel deposited during Pleistocene glacial advances.

The outwash deposits are found along and above major creeks, streams and rivers

Geotechnical Investigation and Seismic Hazard Study 2. Project No.: 2181111-102

Oakridge, Oregon Oakridge School District in the area. The tuffaceous volcaniclastic rocks include variations of tuff or tuff breccia of andesitic to rhyodacite composition.

Based on our current explorations at the site, we believe the subsurface conditions encountered are consistent with the mapped, local geology. Details of the subsurface conditions are provided in the Subsurface Conditions section below and in the exploration logs (Appendix B).

FIELD EXPLORATION

We drilled two exploratory boreholes (BH-3 and BH-4) in the paved area north of the gym on November 5, 2018. At that time, the focus was to evaluate the foundation conditions within the proposed addition footprint.

For this current phase of work, we drilled an additional boring (BH-5) to evaluate the foundation conditions south of the gym and to provide a deeper subsurface profile in support of the seismic hazard study. The approximate boring locations relative to the existing school buildings are shown on Figure 2A (Appendix A).

BH-3 and BH-4 were drilling using a Big Beaver, trailer-mounted drill and BH-5 was drilled using a CME-75, truck-mounted drill. BH-3 and BH-4 extended to a maximum depth of ±6.5 feet and terminated in very dense silty/sandy gravel. In BH-5 extended to a depth of ±24.6 feet. Smooth, sustained hard drilling was encountered below ±24 feet, suggesting the boring potentially terminated on a boulder or on bedrock. Samples were obtained in all borings at 2.5-foot or 5-foot intervals. Disturbed samples were obtained using a split-spoon sampler in conjunction with the Standard Penetration Test (SPT). The SPT provides an indication of the relative stiffness or density of the foundation soils.

The boreholes were continually logged during drilling. The final logs (Appendix B) were prepared based on a review of the field logs, the laboratory test results, and an examination of the soil samples in our office.

DISCUSSION OF SITE CONDITIONS

Site Topography and Surface Conditions

No topographic information was available at the time this report was prepared.

However, the site surrounding the school is relatively flat with a slight dip from north to south. The seismic retrofit portion of the school is surrounded by paved areas to the north and south, by the school to the east, and by grass to the west.

Subsurface Conditions

The following provides a brief description of the subsurface conditions encountered in each boring. Additional details are provided on the appended logs.

Geotechnical Investigation and Seismic Hazard Study 3. Project No.: 2181111-102

Oakridge, Oregon Oakridge School District

BH-3 was drilled near the northeast corner of the locker room building. Drilling at this location encountered ±2 inches of asphaltic concrete (AC) underlain by dense, sandy gravel with some silt (fill) to ±3 feet. Glacial outwash deposits consisting of very dense silty gravel with some sand extends below the fill ±6.5 feet, the limits of the exploration.

BH-4 was drilled near the northeast corner of the gym and southwest corner of the auditorium. Drilling at this location encountered ±2.5 inches of AC underlain by stiff, low to medium plasticity sandy silt (alluvium) to ±3.5 feet. Glacial outwash deposits consisting of dense, silty, sandy gravel extends below the alluvium to

±5.5 feet, the limits of the exploration.

BH-5 was drilled near the southwest corner of the locker room building. Drilling at this location encountered fill consisting of medium dense crushed gravel to ±2 feet, followed by medium stiff, low plasticity silt with some sand to ±3 feet. Medium stiff, low to medium plasticity sandy silt (alluvium) extends below the fill to ±9 feet, followed by glacial outwash deposits consisting of very dense sandy gravel with some silt to ±24.6 feet, the limits of the exploration.

The school is located ±340 feet south of a steep, south-facing slope. Bedrock outcrops were observed along the lower portion of the slope. We reviewed a series of well logs located within the project vicinity. One well log located east of the school near the base of the slope, indicated bedrock was encountered at a depth of

±29 feet. Well logs located further away from the slope (i.e., to the south) encountered coarse-grained deposits to depths of at least ±75 feet. Based on the location of the project site relative to the hillside, we anticipate the area is underlain by coarse-grained glacial outwash deposits followed by bedrock within ±100 feet of the ground surface. Based on the local geologic mapping and samples taken from the outcrops along the slopes north of the school, we estimate the bedrock is tuffaceous, volcaniclastic rocks of the Little Butte Volcanics.

Groundwater

No groundwater was encountered in BH-3 and BH-4 during drilling. Mud-rotary drilling techniques precluded an accurate groundwater measurement in BH-5. Well log information in the project vicinity suggests the static water level ranges from

±15 to 30 feet below the ground surface.

LABORATORY

The laboratory testing included moisture contents and percent fines tests to help classify the soils and estimate their overall engineering properties. The results of these tests are summarized in Table 1C (Appendix C). The moisture contents are also shown on the appended boring logs.

Geotechnical Investigation and Seismic Hazard Study 4. Project No.: 2181111-102

Oakridge, Oregon Oakridge School District

SEISMIC ANALYSIS AND EVALUATION

Seismic-Geologic Site Hazards

In accordance with ASCE 41-17, Section 8.2.2 and OSSC Section 1803.6.1, we reviewed the potential seismic-geologic site hazards including fault rupture, liquefaction, lateral spread, seismically-induced settlement, seismically-induced landslides (i.e., slope instability), and flooding or inundation. The evaluation of the local seismic hazards is provided in the Seismic Hazard Study report (Appendix D).

The findings of the study indicate no seismic hazards at this site.

Site Response Spectra

Design spectral acceleration response parameters were developed for the site in accordance with ASCE 41-17, Section 2.4. The design response spectra prescribed by this code are based on ground motions associated with specific Seismic Hazard

Levels corresponding to defined Performance Objectives. ASCE 41 identifies four specific Seismic Hazard Levels:

• BSE-2N acceleration parameters correspond to the Risk-Targeted Maximum

Considered Earthquake (MCER) ground motions, as defined in ASCE 7-16 and

OSSC 2019.

• BSE-1N acceleration parameters correspond to two-thirds of the MCER.

These parameters are equal to the design-level parameters in ASCE 7-16 and

OSSC 2019.

• BSE-2E acceleration parameters correspond to USGS 2014 ground motion maps with a 5% probability of exceedance in 50 years (i.e., a ±975-year mean return period).

• BSE-1E acceleration parameters correspond to USGS 2014 ground motion maps with a 20% probability of exceedance in 50 years (i.e., a ±225-year mean return period).

The spectral accelerations on rock (SS and S1) were multiplied by Site Class coefficients (Fa and Fv) to develop the surface spectral accelerations based on

ASCE 7-16 Chapter 20. Based on the subsurface profile encountered in BH-5 and a review of local well logs, we have concluded a Site Class C (very dense soil and soft rock) is appropriate for design. Design parameters for the various Seismic

Hazard Levels are summarized in Table 1. The response spectra based on a Site

Class C and 5% structural damping are shown on Figure 3A (Appendix A).

Geotechnical Investigation and Seismic Hazard Study 5. Project No.: 2181111-102

Oakridge, Oregon Oakridge School District

Table 1. Seismic Design Parameters for Selected Seismic Hazard Level

Seismic

Hazard Level

Criteria

Site

Class

SS

S1

Fa

Fv

SXs

SX1

BSE-2N ASCE 7 MCER C 0.52 0.29 1.29 1.50 0.67 0.43

BSE-1N 2/3 ASCE 7 MCER C 0.52 0.29 1.29 1.50 0.45 0.29

BSE-2E 5%/50 years C 0.36 0.20 1.30 1.50 0.47 0.30

BSE-1E 20%/50 years C 0.12 0.06 1.30 1.50 0.16 0.08

Notes:

1. Seismic Hazard Level criteria are defined in ASCE 41-17, Section 2.4.

2. MCER is defined in ASCE 7-16, Section 11.4, as the Risk-Targeted Maximum Considered Earthquake.

3. Short-period (SS) and 1-second (S1) spectral accelerations on rock were determined based on the USGS 2014

Seismic Hazard Maps used in ASCE 7-16.

4. Site Class was determined based on ASCE 7-16 Chapter 20. Site class coefficients, Fa and Fv, were determined based on ASCE 7-16 Tables 11.4-1 and 11.4-2.

5. Site-adjusted spectral acceleration parameters, SXS and SX1, are equal to SSFa and S1Fv, respectively.

Liquefaction

Liquefiable soils typically consist of saturated, loose sand and non-plastic to low plasticity silt. The subsurface profiles encountered in the borings suggest the existing school building is underlain by a thin layer of medium stiff sandy silt

(alluvium) followed by dense to very dense gravel with variable silt and sand content

(glacial outwash deposits). The alluvium is not considered liquefiable due to its fines content and location above the water table and the glacial outwash materials are also not considered liquefiable due to their density. Therefore, there is no liquefaction hazard at the site.

ENGINEERING ANALYSIS

Discussion of Existing Foundations and New Foundations

The locker room and gym sections of the school were built in 1974 and the auditorium building was built in 1976. The buildings are supported on shallow spread footings and continuous wall footings with slab-on-grade floors. As-built drawings prepared by Harlan, Gessford & Erichsen/Architects & Engineers, P.C.

(HG&E) indicate the continuous wall footings have widths ranging from ±1.5 to

4.5 feet and isolated column footings with plan dimensions ranging from

±2.5x2.5 feet to ±8x8 feet. The footings typically extend ±2.5 to 4.5 feet below the finish floor and are underlain by ±18 to 24 inches of compacted engineered fill.

The drawings also indicate the footings were backfilled with gravel fill.

Details of the proposed seismic improvements and loads were not available at the time this report was prepared. Therefore, for analysis and design, we assumed the seismic retrofit improvements may include shear walls and/or new braced frames, and the widening of existing footings to increase seismic resiliency throughout the structures.

Geotechnical Investigation and Seismic Hazard Study 6. Project No.: 2181111-102

Oakridge, Oregon Oakridge School District

Anticipated Foundation Conditions

The explorations indicate the thickness of the surficial sandy silt layer varies between the north and south sides of the buildings. At the north side of the gym, stiff sandy silt was encountered in BH-4 to a depth of ±3.5 feet. South of the gym in BH-5, medium stiff sandy silt extends to a depth of ±9 feet. Dense to very dense sandy/silty gravel (glacial outwash material) was encountered beneath the alluvium in BH-4 and

BH-5, and beneath the AC and fill in BH-3. Based on the variable thickness of the alluvium, we anticipate the new footings will bear on sandy silt or silty, sandy gravel.

Therefore, for design we conservatively assumed all footings bear on sandy silt to reflect the potential variability in the thickness of this layer across the site.

Bearing Capacity

We estimated the bearing capacity for new and existing footings assuming drained conditions, an internal friction angle () of 30 degrees and a moisture unit weight (m) of 110 pcf for the foundation soils. Our calculations indicate allowable bearing pressures of 2,500 psf for continuous wall footings and 3,000 psf for isolated spread footings. The calculated pressures include a typical factor of safety of 3. A one-third increase in the allowable bearing pressure may be used in the evaluation of transient loads (i.e., wind and seismic loads).

Settlement

The existing gym, auditorium, and locker room buildings were constructed several decades ago. Therefore, any settlement beneath existing footings has already occurred. For new footings, we estimate the total settlement could be up to ½ inch and will likely occur as the footings are loaded.

Sliding Coefficient and Passive Resistance for Footings

A sliding coefficient of 0.35 is recommended to analyze the sliding resistance of the existing footings. This value assumes the base of the footings bear on compacted engineered fill. A sliding coefficient of 0.5 is recommended to analyze the sliding resistance of new footings constructed on a minimum of 12 inches of compacted

Select Fill (defined below).

Passive resistance of the soil in front of buried footings was calculated as an equivalent fluid density. An equivalent fluid density of 150 pcf is recommended for the evaluation of new and existing footings, assuming granular fill was used to backfill the existing footings and that compacted Select Fill will be used to backfill the new footings. A factor of safety has been applied to these values, since it is unlikely the footings will move laterally enough to mobilize the full passive resistance.

Geotechnical Investigation and Seismic Hazard Study 7. Project No.: 2181111-102

Oakridge, Oregon Oakridge School District

RECOMMENDATIONS

Construction recommendations provided below assume any required earthwork will occur during dry weather. Depending on the actual time of year construction begins, modifications to the following recommendations may be required. Interior foundation work should not be substantially impacted by exterior weather conditions.

General Earthwork and Material Recommendations

1. Select Fill as defined in this report should consist of 1 or ¾-inch minus, clean (i.e., less than 5% passing the #200 U.S. Sieve), well-graded, crushed gravel or rock.

2. Compact the Select Fill in loose lifts not exceeding 12 inches. Thinner lifts (8 inches or less) will be required where light or hand-operated equipment is used. Compact the Select Fill to a minimum of 95% relative compaction. The maximum dry density of ASTM D 698 should be used as the standard for estimating relative compaction. Field density tests should be run frequently to confirm adequate compaction of the fill.

3. Provide shoring for all trenches to protect workers from sloughing or caving soils. Assume an OR-OSHA Type C soil for planning utility trenching and/or shoring (OR-OSHA, 2011).

Design and Construction of New Footings

We recommend new footings for shear walls and braced frames (and any other new footings), and the widening of existing footings be designed in general accordance with the following recommendations.

4. Design the new foundations and structural upgrades using the seismic parameters provided in Table 1 and shown on Figure 3A (Appendix A).

5. Design new or widened isolated column footings using an allowable bearing pressure of 3,000 psf and new or widened continuous wall footings using an allowable bearing pressure of 2,500 psf. A one-third increase in the allowable bearing pressure may be assumed for transient

(i.e., wind and seismic) loading. These values assume all footings will be constructed on 12 inches of Select Fill.

6. Assume new footings could settle up to ½ inch. Differential settlement between new and existing footings may also be up to ½ inch.

7. Use a coefficient of friction of 0.5 for new footings bearing on Select Fill for sliding analysis.

8. Use an allowable passive resistance of 150 pcf if the footings are backfilled with compacted Select Fill.

Geotechnical Investigation and Seismic Hazard Study 8. Project No.: 2181111-102

Oakridge, Oregon Oakridge School District

9. Excavate for new footings using an excavator equipped with a smooth-edged bucket. The excavation should extend to the depth required to accommodate 12 inches of Select Fill beneath the footings that extends at least 6 inches beyond the edges of the new footings.

10. Backfill the new footing excavations with compacted Select Fill. New footings should be underlain by at least 12 inches of Select Fill. Where existing footings are to be widened, the thickness of the Select Fill should match the existing thickness of granular fill beneath the existing footings.

The foundation conditions beneath new or widened footings should be observed and approved by a representative of Foundation Engineering before being backfilled with Select Fill.

Evaluation of Existing Footings

We recommend evaluating existing footings using the design parameters provided under the Engineering Analysis section for existing footings. The design assumptions stated in that section should be noted unless additional information becomes available that would change our design assumptions.

DESIGN REVIEW/CONSTRUCTION OBSERVATION/TESTING

Foundation Engineering should be provided the opportunity to review all drawings and specifications that pertain to new foundations or the retrofit of existing foundations. We recommend we be present to confirm the soil conditions beneath any new or widened footings prior to backfilling. Mitigation of any unexpected foundation conditions such as unsuitable fill, high plasticity clay, soft soils, or persistent ground water infiltration will also require engineering review and judgment.

That judgment should be provided by one of our representatives.

VARIATION OF SUBSURFACE CONDITIONS, USE OF THIS REPORT, AND WARRANTY

The analyses, conclusions, and recommendations contained herein assume the soil conditions encountered in the borings are representative of the overall site conditions.

The above recommendations assume we will have the opportunity to review final drawings and be present during construction to confirm the assumed foundation conditions. No changes in the enclosed recommendations should be made without our approval. We will assume no responsibility or liability for any engineering judgment, inspection, or testing performed by others.

Geotechnical Investigation and Seismic Hazard Study 9. Project No.: 2181111-102

Oakridge, Oregon Oakridge School District

This report was prepared for the exclusive use of the Oakridge School District, PIVOT

Architecture, and the design consultants for the Oakridge HS Gym & Auditorium

Seismic Retrofit project in Oakridge, Oregon. Information contained herein should not be used for other sites or for unanticipated construction without our written consent. This report is intended for planning and design purposes. Contractors using this information to estimate construction quantities or costs do so at their own risk. Our services do not include any survey or assessment of potential surface contamination or contamination of the soil or ground water by hazardous or toxic materials. We assume those services, if needed, have been completed by others.

Climate conditions in western Oregon typically consist of wet weather for almost half of the year (typically between mid-October and late May). It is assumed adequate drainage will be provided for all new construction. The recommendations for site preparation and foundation drainage are not intended to represent any warranty (expressed or implied) against the growth of mold, mildew, or other organisms that grow in a humid or moist environment.

Our services do not include any survey or assessment of potential surface contamination or contamination of the soil or ground water by hazardous or toxic materials. We assume that those services, if needed, have been completed by others. Our work was done in accordance with generally accepted soil and foundation engineering practices. No other warranty, expressed or implied, is made.

We hope this memorandum meets your current needs. Please do not hesitate to call with any questions.

Geotechnical Investigation and Seismic Hazard Study 10. Project No.: 2181111-102

Oakridge, Oregon Oakridge School District

REFERENCES

ASCE, 2017, ASCE 41-17, Seismic Evaluation and Retrofit of Existing Buildings, American Society of Civil Engineers (ASCE).

ASTM, 2009, Standard Test Method for Description and Identification of Soils

(Visual-Manual Procedure): American Society of Testing and Materials (ASTM)

International, ASTM Standard D2488, DOI: 10.1520/D2488-09A, 11 p.

ASTM, 2011, Standard Test Method for Classification of Soils for Engineering

Purposes (Unified Soil Classification System, USCS): American Society of

Testing and Materials (ASTM) International, ASTM Standard D2487, DOI:

10.1520/D2487-11, 11 p.

IBC, 2016, International Building Code: International Code Council, Inc., Sections

1613 and 1803.3.

OR-OSHA, 2011, Oregon Administrative Rules, Chapter 437, Division 3 -

Construction, Subdivision P – Excavations: Oregon Occupational Safety and

Health Division (OR-OSHA).

Orr, E. L., and Orr, W. N., 1999, Geology of Oregon, Kendall/Hunt Publishing

Company, Fifth Edition, 254 p.

OSSC, 2019, Oregon Structural Specialty Code (OSSC): Based on IBC 2016, Sections 1613 and 1803.3.

Sherrod, D. R., 1991, Geologic Map of a Part of the Cascade Range Between

Latitudes 43°- 44°, Central Oregon: U. S. Geological Survey (USGS), Miscellaneous Investigations Series Map I-1891, 14 p, Scale = 1:125,000.

Appendix A Figures

Professional Geotechnical Services

4,0002,0001,000

SCALE IN FEET

SITE

Foundation Engineering, Inc.

Professional Geotechnical Services

FIG 1A - VICINITY MAP (9-21-20).dwg

Sep. 21, 2020

PROJECT NO.

FIGURE NO.

DRAWN BY:DATE:

VICINITY MAP

OAKRIDGE HS GYM & AUDITORIUM SEISMIC RETROFIT

OAKRIDGE, OREGON

MDM2181111-102

1A

Note: Base map obtained from USGS.

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Notes:

1. The General Procedure Response Spectra are based on ASCE 41-17, Section 2.4.

2. The following parameters are based on USGS 2014 Seismic Hazard Maps and the

ASCE 7 Risk-Targeted Maximum Considered Earthquake (MCER) ground motion maps:

Site Class= C Damping = 5% B1 = 1.0

BSE-2N SS = 0.52 Fa = 1.29 SXS = 0.67 T0 = 0.13

S1 = 0.29 Fv = 1.50 SX1 = 0.43 TS = 0.65

BSE-1N SS = 0.52 Fa = 1.29 SXS = 0.45 T0 = 0.13

S1 = 0.29 Fv = 1.50 SX1 = 0.29 TS = 0.65

BSE-2E SS = 0.36 Fa = 1.30 SXS = 0.47 T0 = 0.13

S1 = 0.20 Fv = 1.50 SX1 = 0.30 TS = 0.63

BSE-1E SS = 0.12 Fa = 1.30 SXS = 0.16 T0 = 0.11

S1 = 0.06 Fv = 1.50 SX1 = 0.08 TS = 0.53

3. Fa and Fv were selected based on ASCE 7-16 Tables 11.4-1 and 11.4-2 and the Site Class.

4. Site location is: Latitude 43.7485, Longitude -122.4698.

FIGURE 3A

ASCE 41-17 SITE RESPONSE SPECTRA

Oakridge HS Gym & Auditorium Seismic Retrofit

Oakridge, Oregon

Project 2181111-102

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 0.5 1 1.5 2 2.5 3

S p e c tr a l A c c e le ra ti o n

S a (g

Period (seconds)

BSE-2N

BSE-2E

BSE-1N

BSE-1E

Appendix B Boring Logs

EXPLORATION LOGS

SYMBOL KEY

DISTINCTION BETWEEN FIELD LOGS AND FINAL LOGS

A field log is prepared for each boring or test pit by our field representative. The log contains information concerning sampling depths and the presence of various materials such as gravel, cobbles, and fill, and observations of ground water. It also contains our interpretation of the soil conditions between samples.

The final logs presented in this report represent our interpretation of the contents of the field logs and the results of the sample examinations and laboratory test results. Our recommendations are based on the contents of the final logs and the information contained therein and not on the field logs.

VARI…