PCI 6 th Edition Preliminary Component Selection

PCI 6th EditionPCI 6th Edition

Preliminary Component Selection

Presentation OutlinePresentation Outline

• Building optimization• Preliminary sizing• Load tables• Additional gravity loading considerations• Fire Resistance considerations• Vibration considerations• Thermal considerations

Building OptimizationBuilding Optimization

• Maximize repetitive and modular dimensions

• Use simple spans• Standardize openings• Use local component sizes• Minimize component types and sizes


• Consider tolerances in connection design• Avoid over specifying design requirements

– Allowable stresses– Allowable cambers– Allowable Deflections– Coatings on reinforcing steel– Embedded hardware– Loose Connection hardware


• Use of exterior wall panels as load bearing components and structural walls

• Maximize form use and minimize form differences / variation

• Contact a local producer as early as possible during the design development stages of a project for assistance and answering questions

Why estimate component size?Why estimate component size?

• To verify the product fits the application

• Establish floor to floor height

• Establish floor area

• To estimate project cost

Preliminary Analysis Should Include:Preliminary Analysis Should Include:

• Framing dimensions• Span-to-depth ratios• Connection concepts• Gravity and lateral load resisting system• Mechanisms for the control of volume

changes

Preliminary Span to Depth RatiosPreliminary Span to Depth Ratios

• Hollow-core– Floor slabs 30 to 40– Roof slabs 40 to 50

• Stemmed Components and Solid Slabs– Floor 25 to 35– Roof 35 to 40

• Beams 10 to 20

Load Table AssumptionsLoad Table Assumptions

• Flexural strength

• Shear strength

• Release stresses

• Stress limits under service loads

Flexural Strength ControlFlexural Strength Control

• Equivalent uniform load

• Evaluated at critical moment sections

• Load factors: 1.2D + 1.6L

• Strength reduction factor: = 0.9

Release Stress LimitsRelease Stress Limits

• Compression limit:

• Tension limit:

7fc̀

6 fc̀

Service Loading Stress LimitsService Loading Stress Limits

• Extreme fiber in compression – Prestress plus sustained loads: 0.45f’c

– Prestress plus total load: 0.6f’c

• Extreme fiber in tension – Double tees and beams: – Flat Deck Members:

12 fc̀

7.5 fc̀

Shear Strength ControlShear Strength Control

• Load Factor: 1.2D + 1.6L

• Strength Reduction Factor: = 0.75

Beam Load TablesBeam Load Tables

• Loading is uniform

• Strength design - same as double tees

• Stress limits - same as double tees

Load Table In-depthLoad Table In-depth

PCI Design Handbook, 6th Edition Page 2-16

Load Table In-depthLoad Table In-depth

• Section dimensions• Section properties• Material properties• Strand geometry• Depression points

Load TableLoad Table








Load Table ExampleLoad Table Example

Given:Section geometry and material properties• 10DT24 roof tee• Lightweight concrete• f’c = 5000 psi• f’ci min = 3500 psi• Design length = 58’-6”


Given:Design Loads• Superimposed Dead Load = 10 psf (roofing)• Superimposed Live Load = 30 psf (snow)Total Service Load = 40 psf (for design tables)

Problem:• Determine a suitable strand pattern from load

tables

PCI Design Handbook, 6th Edition Page 2-16


Resulting Strand PatternResulting Strand Pattern

• (8) ½” 270ksi strands

• Straight strand pattern

• 2.6” Camber at erection

• 2.2” Camber long term

• Assumptions– Initial pull = 0.75fpu

– Initial losses = 10%

– Total losses = 20%

• Always develop a final design based on specific conditions

Load TablesLoad Tables

• Limitations– Special materials

• Concrete• Strand

– Unique geometry• Pie shaped pieces• Blockouts

– Special or unique loading conditions

– Fire truck loading

Additional Loading ConsiderationsAdditional Loading Considerations

• Snow

• Drifting loads


• Snow

• Drifting loads

• Corridor loads

• Walkways


• Snow

• Drifting loads

• Corridor loads

• Walkways

• Impact

• Combination of load


• Snow• Drifting loads• Corridor loads• Impact• Combination

of load• Beware of piling snow

– Add Snow gate/chute

Fire Resistance ConsiderationsFire Resistance Considerations

• Time Ratings• Based on

– Square footage– Building type– Cover

Requirements

Fire Resistance ConsiderationsFire Resistance Considerations

• Three Methods to Determine Fire Resistance Rating– Testing (§703) – ASTM E

119– Prescriptive (§720)– Calculated (§721)

Office Building ExampleOffice Building Example

Given:– Exterior bearing wall system– Floor system

Assumptions– Unlimited area potential– Using prescriptive methods

Problem:– Determine required wall and floor resistance

requirements and reinforcing cover

Solution StepsSolution Steps

Step 1 - Determine group classification

Step 2 - Determine construction type based on building area and available footprint

Step 3 - Determine component resistance requirements

Step 4 - Determine reinforcing cover requirements

Step 1 – Group Occupancy ClassificationStep 1 – Group Occupancy Classification

• Section 303– IBC 2003

• Group Classification– Group A – Assembly– Group B – Business– Group E – Educational– Group F – Factory– Group H – High Hazard– Group I – Institutional– Group M – Mercantile– Group R – Residential– Group S – Storage– Group S-2 – Parking Garage– Group U – Other / Utility

Step 2 – Determine Construction TypeStep 2 – Determine Construction Type

• Table 503 IBC 2003– Allowable Height and

Building Areas

• Based on– Building Group– Building Size

• Group – B• Unlimited Footprint• Construction Type

Type I - B

Step 3 – Wall Resistance RequirementsStep 3 – Wall Resistance Requirements

• Table 602– IBC 2003

• Function of Building Element and Construction Type

• Example – – Exterior Bearing Wall– Type I B 2 hour

• Table 602– IBC 2003

• Function of Building Element and Construction Type

• Example – – Floor

Construction– Type I B

2 hour

2 hour

Step 3 – Wall Resistance RequirementsStep 3 – Wall Resistance Requirements

Step 4 – Thickness of Insulating Material - WallStep 4 – Thickness of Insulating Material - Wall

• Table 720.1– IBC 2003

Step 4 – Thickness of Insulating Material - FloorStep 4 – Thickness of Insulating Material - Floor

• Table 720.1– IBC 2003

Example ConclusionExample Conclusion

• Office– Unlimited Area– Maximum 11 Stories / 160 ft

• Type IB Construction• Exterior Bearing Wall

– 2 hours– 1 ½” Cover

• Floor System– 2 hours– 2 ½” Cover

Code Endurance Table ExampleCode Endurance Table Example

Given:The following Double Tee (page 9-49)Assumptions– Strands are ½” diameter– Siliceous aggregate– Normal weight concrete– Topped System – Restrained

Problem:For a 2 hr rating determine– The strand cover required– Floor Thickness required


Step 1 – Determine effective cross sectional area and associated cover

requirements

Step 2 – Compare to cover provided

Step 3 – Determine heat transfer requirements and compare to provided conditions

Step 1 – Effective Area and Required CoverStep 1 – Effective Area and Required Cover

• Table 9.3.7.1(5) (Page 49)• Average Stem Width

(3.75 + 5.75)/2 = 4.75 in• Effective Flange width = 3 x Avg Stem

3(4.75) = 14.25 in.• Aeff = 22(4.75)+14.25(5)=175.75 in2

Step 2 – Supplied CoverStep 2 – Supplied Cover

• Side cover provided [3.75 + (3.5/22)(5.75–3.75) – 0.5]/2 = 1.78 in

• Bottom cover provided2 – 0.5/2 = 1.75 in

• Both exceed 1 ½ in OK

Step 3 – Heat TransferStep 3 – Heat Transfer

• Per Figure 9.3.6.15 in Minimum

• Provided 2 in tee flangeand3 in topping= 5 in total

Vibration ConsiderationsVibration Considerations

• Causes– Machinery– Exercise– Cars– Walking– Impact

Minimize Vibration or AffectsMinimize Vibration or Affects

The goalDecrease the amplitude of the vibration

OR

Decrease the Systems Natural Frequency

• Decrease Span• Increase Mass

Vibration SolutionVibration Solution

• Based on minimum natural frequencies

• Calculations are approximate as estimation of damping and human response is varied

Types of Analysis MethodsTypes of Analysis Methods

• Based on excitation– Walking– Rhythmic Activities– Mechanical Equipment

Natural FrequencyNatural Frequency

• Vibration limits are a function of Natural Frequency, fn

Where

g – Acceleration due to gravity

– Displacement of system

fn∝

g

⎛

⎝⎜

⎞

⎠⎟

Minimum fnMinimum fn

• Floors with natural frequencies lower than 3 Hertz are not recommended

• People may more readily synchronize their actions at lower frequencies

DampingDamping

• Handbook references are based on modal damping

• Highly dependent on the non-structural items– Partitions– Ceilings– Furniture

HarmonicsHarmonics

• Higher modes of vibration

• Deal with – Rhythmic Activities – Oscillating Equipment

Office DT ExampleOffice DT Example

Given:– 10DT32+2

• Page 2-18

– Open office area– 60-ft span

Problem:– Check for vibration

caused by walking.

SolutionSolution

• Find the systems minimum Natural Frequency, fn and compare it to the Fundamental Frequency, f

f ≥ fn


Step 1 – Establish natural frequency equation

Step 2 – Determine natural frequency parameters

Step 3 – Calculate the effective weight

Step 4 – Calculate natural frequency

Step 5 – Determine expected system frequency

Step 1 – Establish Natural FrequencyStep 1 – Establish Natural Frequency

• Systems Natural Frequency - Empirical formula based on walking

• Represents smallest natural frequency to prevent disturbance

• Equation 9.7.6.1

Where:

W – Effective Weight

K, – factor representing structure type and damping

fn≥2.86 ln

K

W

⎛

⎝⎜⎞

⎠⎟⎡

⎣⎢⎢

⎤

⎦⎥⎥

Units of 2.86 are 1/sec

Step 2 – Natural Frequency ParametersStep 2 – Natural Frequency Parameters

• K and – Table 9.7.6.1 (pg 9-69)

Footnotes: a. For floors with few non-structural components and furnishings, open work area, and churches b. For floors with non-structural components and furnishings, cubicles c. For floors with full-height partitions

Step 3 – Calculate Effective WeightStep 3 – Calculate Effective Weight

• Effective Weight (W) W = w · (Effective Area)

w = supported Load

• Effective Area = [60%(L)] · L = 0.6L2

W=w·0.6l2

Step 3 – Calculate Effective WeightStep 3 – Calculate Effective Weight

• Supported Load– Superimposed Load - Assume 10 psf– Dead Load - Double Tee + Topping

• Effective Weight

W=w⋅0.6l2 =99psf ⋅0.6 ⋅ 60ft( )

2=214kips

w =64psf +2in

12 inft

⋅150pcf +10psf =99psf

Step 4 – Calculate Natural FrequencyStep 4 – Calculate Natural Frequency

• Recall

fn≥2.86 1

secln

13kips

0.2 ⋅214kipskips

⎛

⎝⎜⎞

⎠⎟⎡

⎣⎢⎢

⎤

⎦⎥⎥

=3.18hz

fn≥2.86 ln

K

W

⎛

⎝⎜⎞

⎠⎟⎡

⎣⎢⎢

⎤

⎦⎥⎥

Step 5 – Expected Fundamental FrequencyStep 5 – Expected Fundamental Frequency

• Fundamental Frequency of selected floor unitsFigure 9.7.4.1 (Page 9-68)

3.8

Example ConclusionExample Conclusion

• Calculated Minimum Natural Frequencyfn = 3.18hz

• Expected Fundamental Frequencyf = 3.8hz

f ≥ fn - Therefore OK

Thermal ConsiderationsThermal Considerations

• Thermal Calculations– Thermal Resistance: R -Values– Heat Transmittance: U - Values

• Thermal Lag or Storage –– Significant benefit of Precast Concrete

Construction

• Moisture Control• Thermal Bridging

Thermal CalculationsThermal Calculations

• Thermal Resistance: R -Values– Example Table 9.1.4.1– Page 9-7

Thermal CalculationsThermal Calculations

• Heat Transmittance:– U - Values

U =

1R∑

Thermal Lag or StorageThermal Lag or Storage

• Thermal Lag or Storage –– Significant benefit of

Precast Concrete Construction

Moisture Control DiscussionMoisture Control Discussion

• Air Barriers

• Vapor Retarder

Air BarriersAir Barriers

• Continuity throughout the building envelope

• Ability to support a differential air pressure

• Must be virtually air impermeable• Must be durable

Vapor Retarder Vapor Retarder

• Low permeability materials

• Stop or retard the passage of moisture

Typical Wythe Connection MethodsTypical Wythe Connection Methods

• Wythe Ties

• Solid Zones

PurposePurpose

• To create larger section properties for structural considerations

• Maintain structural integrity between the multiple wythes of concrete

Thermal BridgingThermal Bridging

• Direct Link / Bridge through a primary insulating material connecting two or more non-insulating materials

Thermal BridgingThermal Bridging

• Effect of these Bridges– Cold Spots– Condensation Buildup

• Calculating R and U values– Zonal Method – Metal Ties– Characteristic Section Method – Solid Zones

Thermal Bridging CalculationsThermal Bridging Calculations

• Calculating R and U values– Zonal Method – Metal Ties– Characteristic Section Method – Solid

Zones

Preliminary Design BenefitsPreliminary Design Benefits

• Accurate early planning for smooth running schedule and cost control

• Accurate Material Requirements

• Accurate Section Geometry

• Precast design team can provide benefit to the entire project design team

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PCI 6 th Edition Preliminary Component Selection