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Lecture Two- Systems & Paths

SE APPRENTICE

Today’s Speakers

Today’s Moderators

Lisa Willard, PESE Solutions, LLC

Brian Quinn, PESE Solutions, LLC

Carrie Bremer, PESchaefer

Stephen Metz, PESMBH, Inc.

SE Apprentice Content Created by Carrie Bremer & Stephen Metz; Event produced by SE Solutions, LLC

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Lateral Loads

Lateral Loads are usually caused by wind and

seismic loads on buildings. They can also be a result of hydrostatic or soil loads.

The part of the structure that resists lateral loads is called the Lateral Load Resisting

System.

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Lateral Load Systems

Common Lateral Load Resisting Systems

� Braced Frames

� Moment Frames

� Shear Walls- Concrete, Masonry or Wood

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Lateral Load Systems

Demonstration Video

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Braced Frames

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Braced Frames

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Braced Frames

Braced Frame Configurations

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Moment Frames

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Moment Frames

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Shear Walls

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Shear Walls

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Shear Walls

� Shear � Moment

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Stability

� Sliding � Overturning

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Serviceability

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3-story, 60,000 sq. ft. steel-framed office building 200 ft. x 100 ft. with 25 ft. column bays

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Design Examples

Floor Construction Cladding Type Lateral System

Thin slab on bar joists (light)

E.I.F.S. with stud backup (light)

Moment frames (flexible)

Composite slab on steel beams (heavy)

Brick with stud backup (heavy)

Braced frames or shear walls (stiff)

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Design Example Variables

Case Floor Construction Cladding Type Lateral System

1 Light Light Flexible

2 Light Heavy Stiff

3 Heavy Heavy Stiff

4 Heavy Heavy Flexible

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Design Example Cases

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Case 1: Light floor with moment frames (Case 4 is similar)

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CaseCs

coefficient

Building Weight, W

(kips)

Base Shear, V (Cs*W, kips)

Seismic Horizontal

Deflection, d**

Effective Steel

Tonnage (Tons)

1: L-L-F 0.037 2,752 100.0 1.85” 177

2: L-H-S 0.060 3,487 207.0 0.52” 176

3: H-H-S 0.060 4,096 243.2 0.49” 217

4: H-H-F 0.037 4,096 148.9 2.23” 251

**Wind deflection limit of 1.26” controlled in the short direction with a wind base shear of 147 kips

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Design Example Results

1. Light floor – Light cladding – Flexible lateral system

2. Light floor – Heavy cladding – Stiff lateral system

3. Heavy floor – Heavy cladding – Stiff lateral system

Most Economical

Least Economical 4. Heavy floor – Heavy cladding – Flexible lateral system

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Design Example Costs Hierarchy

Shear walls can double as bearing walls and vise-versa, further reducing steel frame tonnage and saving money

Compared to moment frames, braced frames reduce the overall foundation, anchor bolt installation, steel tonnage, and erection costs

Lighter floor and cladding systems reduce seismic loads and steel tonnage

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Keys to Economical Structures

Choosing a System

� Aesthetic Considerations- Exterior Façade, Floor plans, building layout

� Structural System- Lateral load resisting system has to work with the rest of the structural system. For example, we probably won’t use a steel moment frame in wood construction

� Cost

� Constructability and Construction Schedule

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Generator Building

� Braced Frames

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Generator Building

� Braced Frames

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Load Path

Loads applied to the building cladding

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Load Path

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Diaphragms

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Diaphragms

� Flexible or Rigid?

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Diaphragms

� Diaphragms

� Flexible

� Metal deck

� Plywood or OSB sheathing

� Rigid

� Concrete slabs (formed and on metal deck)

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Flexible Diaphragms

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Rigid Diaphragms

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Rigid Diaphragms

P1=V1= w l 2

w

P2=V2= w l 2

I=b d3

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d1= d2

b1= b2

I1= I2

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Rigid Diaphragms

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Generator Building

� Flexible Diaphragm

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Generator Building

� Rigid Diaphragm

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Load Combinations

The building code acknowledges that it is unlikely that the building structure will experience the full magnitude of multiple loads at the same time.

Load combinations are the way the code acknowledges this.

There are two different series of Load Combinations:

Strength Design (LRFD) and

Allowable Stress Design (ASD)

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Load Combinations

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Load Combinations

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Load Combinations

� Different load combinations control for

different pieces and parts of the building. Each building and system component must be designed for the worst case load combination.

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Generator Building

� Braced Frames

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Column Load

PDL= 75psf x 37’ x 27.5’ = 19k 2 2

PLL= 25psf x 37’ x 27.5’ = 6.4k 2 2

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Column Load

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Column Load

W= 21psf x 26’ x 88.75’ = 12k 2 2

PWL= 12k x 26’ / 18.5’ = 17k

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Column Load

1.0 DL+1.0LL 1.0 DL+.75LL+.75WL

PDL= 19k

PLL= 6.4k

PWL= 17k x .75 = 13k

PDL = 19k

PLL= 6.4k x .75 = 4.8k 25.4k

36.8k

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Carrie Bremer carrie.bremer@schaefer-inc.com

(614) 706-5405

www.schaefer-inc.com

Stephen Metz smetz@smbhinc.com

(614) 481-9800

www.smbhinc.com

Questions?

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Which University is the answer to this session’s challenge question?

• Cal Poly, San Luis Obispo

• Oregon State

• Purdue

• The Ohio State University