Design of Buildings 2008

transcript

Principles of Building Design

DPWH Field Engineers Course

Contents of the Presentation:

2. Scope of Building Design

Building Design & Construction Process; FunctionalRequirements; Objectives of Design

Wind/EQ Load Provisions

1. Introduction: Overview

3. Structural Design Methods of Structural Design/Analysis; Loadings4. Structural Design Code Provisions

5. Examples of Building Failures & Their Causes

Required Design Data; Types of Construction;Design Revision

Proposed BuildingBudget, Requirements

Building Plans

Design Professionals/Consultants Planning, Materials, Aesthetics, Cost (Value)

Structural/Civil/GeotechnicalConstruction

PermitsSupervision/InspectionMaintenance Building Design & Construction Process

Architectural

Electrical/MechanicalSanitary/Plumbing

Functional Requirements:1. Friendly and inviting image that has positive values

to building owners, users, and observers2. Fit the site, providing proper approaches to layout

congenial for people to live, work and play3. Energy-efficient, providing space with controllable

climate for its users.4. For office buildings, allow flexibility in office layout

with easily divisible space.5. Offer space oriented to provide the best views.6. Economical

AppropriatenessArrangement of spaces, spans, access, and

traffic flow must complement the intended use.

The structure should fit its environment and be aesthetically pleasing

Objectives of Design:

Economy

Overall cost should not exceed the budget

Teamwork/coordination during planning &design stages will lead to overall

economy

Structural Adequacy

Must be strong enough to safely support allanticipated loadings

Must not deflect, tilt, vibrate, or crack in a manner that impairs its usefulness

Maintainability

Should be designed to require a minimum ofmaintenance.

To be able to be maintained in a simplefashion.

Scope of Building Design

Architectural Design – functional, aesthetics

- Land Use Plan/Zoning Regulations

- Fire Safety

- National/Local Regulations (building codes, ordinances, environmental issues)

Scope of Building Design

Structural/Civil/Geotechnical – stability, serviceability

- Loadings : Gravity, Lateral

- National/Local Regulations (building/structural codes, ordinances, environmental issues)

- Structural Systems/Materials

Scope of Building Design Electrical/Mechanical : functional,

serviceability

- Fire Suppression & Protection, Safety- Lighting Systems-Mechanical requirements: HVAC, Water

Supply

- National/Local Regulations (building codes, ordinances, environmental issues)

Scope of Building DesignSanitary/Plumbing: functional,

serviceability

- Water supply systems

- Sewage/Drainage systems

- National/Local Regulations (building codes, ordinances, environmental issues – sanitation/health)

Planning/Design Phase

1. Site Condition

Location/AccessibilityLot Area/Dimension (Title/Ownership)Available Parking Spaces Subsoil Condition, Terrain Existing Development/Existing

Structures/Utilities Drainage System, Water Supply Power Source

Required Design Data

2. Preliminary Design/Plan & Site Development

Space Organization & Requirements

Occupancy/Usage/AccessParking SpacesSoil Tests ReportsWater Supply SystemsElectro-Mech. SystemsMaterials RequirementsAestheticsInitial Cost/Budget

3. Final Design/PlanDevelopment

Project Cost (Value Engineering)Owner’s Specifications/

Additional Requirements Other Governmental Rules/

Regulations/ConstraintsChanges due to actual site

Condition

Design Output Data

3. Final Design/PlanDevelopment

Final Working Drawings,Detailing &

SpecificationsProject Cost (optimum)

1. Site Condition

2. Preliminary Design/Plan & Site Development

Implementation Phase

Types of Construction (Rule IV, IRR-NBC)Type I : WoodType II : Wood construction with protective

fire-resistant materials and one-hour fire resistance

Type III : Masonry and wood constructionType IV : Steel, Iron, Concrete or Masonry

with ceilings and permanent partitions made of incombustible materials

Type V : Four-hour fire resistance made of Steel, Iron, Concrete or Masonry

Design Revisions:Change in Types

Change in Use/Occupancy

Change in Dimension

Change in Physical Appearance

Change in Foundation Type

Methods of Structural Analysis

Factor Method

Stiffness Method : computer-aided Portal Method

ACI Moment Coefficient Moment Distribution Method

Methods of Structural Design

Ultimate Strength Design (USD)Plastic Design

Load and Resistance Factor Design (LRFD)

Working (Allowable) Stress Design (WSD/ASD)

LoadingsDead Loads – weight of the structure

and permanent attachments Live Loads – maximum loads expected

by the intended use or occupancy Other Loads – impact, fluid pressures, lateral pressure, ponding loads, crane

loads, equipment load, etc.Wind Load Seismic Load

The National Structural Code of the Philippines (NSCP)

Approved as a referral code of the NBCPboth by the DPWH and PRC Board of Civil Engineering

Two (2) volumes are available:

Volume 1: Buildings, Towers and OtherVertical Structures: (5th Ed. 2001)

Volume 2: Bridges: (2nd Ed. 1997)

Structural Design Codes National Structural Code of the Philippines

(NSCP) 2001 Volume 1: Buildings, Towersand Other Vertical Structures

ASEP Steel Handbook ASEP Earthquake Design Manual

Wind Load: Every building and every portion thereof shall be designed and constructed to resist the effects of wind. ( NSCP Sec.207.1)

WIND PRESSURE

Prw Prl

WIND DIR.

Analysis due to Wind

Analysis due to Wind:Allowed Procedures

Analytical Procedure Wind-tunnel Procedure

ANALYSIS DUE TO WIND (ANALYTICAL PROCEDURE):

Location

Velocity Pressure, qz

Wind Speed, Exposure, Topography

Structure Type / Framing System

Enclosure Classification, Internal & External Pressure Coefficients, Importance Factor, Height

Topography, Exposure, Height, Importance Factor, Wind VelocityDesign Wind Force, p; F

Gust Effect Factor, G or Gf Stiffness, Exposure

Frame Analysis Lateral Force Distribution,Load Combinations

Design Wind Pressure, p, on Main Wind-Force Resisting Systems:

Buildings of all heights :p = q GCp – qh(GCpi)

q: qz for windward wall at height z above ground qh for leeward wall, side walls and mean roof

heightG = gust effect factor, = 0.80 for exposures

A and B, and 0.85 for exposures C and DCp – external pressure coefficientGCpi – internal pressure coefficient

Analysis due to Wind (cont.)

Low-rise Buildings > mean roof height, h lessthan or equal to 18 meters or does not exceed least horizontal dimension

p = qh [(GCpf) – (GCpi)]

qh = velocity wind pressure at height z = h, in Kpa taken at mean roof height using Exposure C for all terrain

Design Wind Pressure, p, on Main Wind-Force Resisting Systems :

GCpf, GCpi – internal pressure coefficients

Design Wind Pressure, p, for Open BuildingsAnd other Structures

F = qz GCf Af

qz – at height z above ground G = 0.80 for exposures A and B, and 0.85 for exposures C and DCf – force coefficients given in Tables 207-6

to 207-10Af – projected area normal to wind

Wind Zone Map

Exposure Category: refers to the conditions of the terrain surrounding the building site – variations in ground surface roughness that arise from natural topography and vegetation, as well as from constructed features.

Four (4) categories are given: A, B, C, D

Exposure A – large city centers with at least 50% of the buildings having a height in excess of21 meters.

Exposure B – urban and suburban areas, wooded areas, or other terrain with numerous closely spaced obstructions, having the size of single dwellings or larger

Exposure C - open terrain with scattered obstructions having heights generally less

than9 meters. Includes flat open country andgrasslands.

Exposure D – flat, unobstructed areas exposed to wind flowing over open water for a distanceof at least 2 km.

Enclosure Classification:Partially Enclosed Building:

Total area of openings in a wall that receives positive external pressure exceeds 0.5 sq.m. or 1% of the area of the wall, whichever is smaller, and the percentage of openings in the balance of the building envelope does not exceed 20 %

Total area of openings in a wall that receive positive external pressure exceeds the sum of the areas of openings in the balance of the building envelope by more than 10 %

Open Buildings

Enclosed Building

All walls at least 80% open

Not complying with the requirements for open and partially enclosed building

Enclosure Classification (cont.)

Essential Facilities- hospitals & other medical facilities, fire & police stations, Iw = 1.15Hazardous Facilities- structures housing

toxic or explosive substances , Iw = 1.15 Special Occupancy Structures – for public assembly, schools, Iw = 1.15Standard Occupancy Structures- structures not listed above , Iw = 1.00Miscellaneous Structures, Iw = 0.87

Importance Factor, I

Analysis due to Wind (cont.)Gust Effect Factor, G or Gf

For Rigid Structures

For exposures A and B: G= 0.80For exposures C and D: G= 0.85

For Flexible Structures, Gust Effect Factors, Gf shall be computed by rational analysis

Analysis due to Wind (cont.)Topographic Effects - Wind speed-up effects at isolated hills, ridges, and escarpment constituting abrupt changes in the general topography.

Topographic Factor, Kzt = (1 + K1K2K3)2

WIND PRESSURE

Prw Prl

WIND DIR.

Earthquake Load

Structures and portions thereof shall, as a minimum, be designed and constructed to resist the effects of seismic ground motions. The purpose of the earthquake provisions is primarily to safeguard against major structural failures and loss of life, not to limit damage or maintain function.

NSCP Lateral (Seismic) Forces

The 2001 NSCP introduces the concept of near-source factors.

Proposed structures close to an active fault are to be designed for an increased base shear compared to similar structures located farther from an active fault.

Earthquake Load (cont.)

• Static Lateral Force Procedure

•Dynamic Lateral Force Procedure

•Simplified Static Lateral Force Procedure

Lateral Force (Seismic) Procedure

Analysis due to Earthquake (cont.):

ANALYSIS DUE TO EARTHQUAKE

Location

Frame Analysis

Zone Factor, Seismic Source Type,Distance from the Source, Soil Parameters

Structure Type & Framing System

Importance Factor, Height, Configuration, Period, Near- Source Factors, Lateral-Force Procedure Base Shear, Lateral Force

Distribution (Vertical & Horizontal), Stresses, Drift, P-Delta Effects

Combined Forces EQ (vertical, horizontal), DL, LL

Seismic Zone Map

Table 208-6: Seismic Source TypeType Description Maximum Moment

Magnitude

AFaults that are capable of producing large magnitudeevents and that have a highrate of seismic activity

M = > 7.0

Faults that are not capable of producing large mag. EQs and that have a relatively low rate of seismic activity

B All faults other than A&C 6.5<= M < 7.0

M < 6.5

Seismic Source Types

Distance from the Seismic Source

Site Geology/Soil Characteristics

Soil Profile Type

Description

SA Hard RockSB RockSC Very Dense Soil &

Soft RockSD Stiff SoilSE Soft SoilSF Soil requiring site

specific evaluation

I. Essential Facilities- hospitals & other medical facilities, fire & police stations, etc >> I =

1.25II. Hazardous Facilities- structures housing, supporting or containing quantities of toxic or explosive substances >> I = 1.25

III. Special Occupancy Structures – for public assembly, schools, day care centers >> I = 1.00

IV. Standard Occupancy Structures- structures having occupancy not listed above >> I = 1.00

V. Miscellaneous Structures >> I = 1.00

Seismic Importance Factors

Regular Structures : No significant physical discontinuities in plan or vertical configuration or in their lateral force resisting systems

Configuration Requirements

• Low height-to-base ratio• Balanced resistance• Symmetrical plan• Uniform section and elevation• Maximum torsional resistance• Short spans• Direct load paths• Uniform floor heights

Irregular Structures: Have significant physical discontinuities in configuration or in their lateral force resisting systems

Refer to Table 208-9 & 208-10, NSCP 2001 for Irregularity Types & Definitions

Configuration Requirements

Irregular Structures: Vertical Irregularities

Irregular Structures: Plan Irregularities

REFERENCE TABLE 208-4 (Near-Source Factor Na)

0.0 5.0 10.0 15.0 20.0Distance to Source (km)

Source Type ASource Type B

Table 208-7: Seismic Coefficient, CaSoil Profile Seismic Zone Factor, Z

Z= 0.20

Z= 0.40

SB 0.20

0.240.280.34

0.32Na 0.40Na

0.40Na 0.44Na

0.36NaTo be determined from geotechnical investigation& dynamic site response analysis

Table 208-8: Seismic Coefficient, CvSoil Profile Seismic Zone Factor, Z

Z= 0.20

Z= 0.40

SB 0.20

0.320.400.64

0.32Nv 0.40Nv

0.56Nv 0.64Nv

0.96NvTo be determined from geotechnical investigation& dynamic site response analysis

Simplified Static Lateral Force Procedure

1. Buildings of any occupancy (including singlefamily dwellings) not more than threestories in height excluding basements, that use light-frame construction

2. Other buildings not more than two stories in height excluding basements.

Applies to following structures of OccupancyCategory IV or V:

Analysis due to Earthquake (cont.)

Simplified Design Base Shear, V:

V = -----------3.0 Ca

Fx1= -----------3.0 CaR

Fx2= -----------3.0 CaR

Static Lateral Force Procedure

2. Regular structures under 75 m in height3. Irregular structures not more than five stories nor 20 meters in height

1. All structures, regular or irregular, in Occupancy Category IV or V in Seismic

Zone 2.

Design Base Shear, V:

Cv I V = ----W

Need not exceed:

2.5 Ca I V = ------- W

Shall not be less than:

Shall not be less than ( for Seismic Zone 4 only):

V = 0.11 Ca I W

0.8 ZNvI V = -------- W

STRUCTURE PERIOD,T

Method A:T = Cthn

Ct = 0.0853 for steel moment-resisting frames

= 0.0731 RC moment frames and eccentric braced frames

= 0.0488 for all other buildings hn = height in meters above the base

Approximate Building Periods in seconds (FEMA)

Ft + Fx+3

Vertical Distribution of Force

(V-Ft) Wxhx Fx =-------------- Wihi

Ft=0.07TV <=0.25VFt=0 if T<=0.7 secFx – design seismic force at level xFt – portion of base shear concentrated at topVx= story shear

V = base shear

HORIZONTAL TORSIONAL MOMENT

Torsional Moments:

Mty = Vx N-S (ex+exa)Mtx = Vx E-W (ey+eya)

Vx E-W

VxE-WCM

F = (R/∑R)V ± Mt Rd/∑Rd2 d-dist of each element from CR

Direct Shear Torsional Shear

HORIZONTAL TORSIONAL MOMENT

Drift Limitations – 208.5.10 •T < 0.7s: M ≤ 0.025 h•T ≥ 0.7s: M ≤ 0.020 h

Drift Limitations

Expected Maximum Inelastic Drift – 208.5.9 M = 0.7 R S (208-17)

S - total story drift due to design seismic forces

Story Drift – displacement of one level relative to the level above or below it.

m - total story drift due to design basis ground motion

Building SeparationClear gap between adjacent

buildings MT = (M1

2 + M22 )

ΔM1 & ΔM2 are the displacements of adjacent buildings

P-DELTA EFFECTS

The resulting member forces and moments and the story drifts induced by P-Δ effects shall be considered in the evaluation of the overall structural frame stability.

P-Δ effects need not be considered when the story drift does not exceed 0.02/R.

Secondary Moment /Primary M ≤ 0.10

Δ1 Δ1 Δ2

Va = VMa = V*h

Vb = VMb = (V*h)+(P*Δ1)

Vc=VMc = (V*h)+

P(Δ1+Δ2)Va Vb Vc

Ma Mb Mc

P-DELTA EFFECTS

Dynamic Analysis • Structures 75 m. or more in height• Structures having stiffness, weight or geometric

irregularity • Structures over five stories or 20 meters in height

in Zone 4 not having the same structural system throughout their height • Structures, regular or irregular, located on Soil

Profile Type SF that have a period greater than 0.70 sec. The analysis shall include the effect

of the soil at the site

Load Combinations : Buildings must be designed to sustain without excessive deformation or failure combinations of service loads that will produce the most unfavorable effects.

Note that the most critical effect may occur when one or more of the contributing loads are not acting.

Note: Wind and seismic loads shall not be considered acting simultaneously.

Load Combinations (cont.) :

Earthquake Loads:

E = ρ Eh+Ev Em = Ωo Eh+Ev

E- earthquake loadEh – EQ load due to base shear V

Em – estimated max. earthquake load due to that can be developed in a structureEv – load effect due to vertical component of the earthquake ground motion = 0.5 Ca I DΩo – seismic force amplification factor Table 208-11 ρ – reliability/redundancy factor

A new factor for overstrength Ώo has replaced (3/8) Rw for use in special local cases where the maximum earthquake force is required, such as columns suppoting discontinuous shear walls, weak stories, and collector elements.

Seismic Lateral Force: Overstrength Factor

Em = o Eh o ~ (3/8) Rw

The Ώo factor is therefore applied to the design of elements and connections whose yield or failure could result in local or general collapse.

Load Combinations : LRFD 1.4 D (203-1) 1.2 D + 1.6 L + 0.5 Lr

(203-2) 1.2 D + 1.6 Lr + (f1 L or 0.8 W) (203-3) 1.2 D + 1.3 W + f1 L + 0.5 Lr (203-4) 1.2 D + 1.0 E + f1 L

(203-5) 0.9 D ± (1.0 E or 1.3 W) (203-

6) D - dead load L - live load W – wind

load Lr – roof live load E - earthquake load f1 = 1.0 for floors in places of public assembly,

for live loads in excess of 4.8kpa, and for

garage live load = 0.5 for other live loads

D - dead load L - live load W – wind load Lr – roof live load E - earthquake load f1 = 1.0 for floors in places of public assembly,

for live loads in excess of 4.8kpa, and for garage live load

= 0.5 for other live loads

Load Combinations : RC & Masonry 1.4 D + 1.7 L (409-1) 0.75 (1.4 D + 1.7 L + 1.7 W) (409-2) 0.9 D + 1.3 W (409-3) 1.32 D + 1.1 f1 L + 1.1 E

(409-4) 0.99 D ± 1.1 E

(409-5)

Load Combinations: Allowable Stress Design

D (203-7)

D + L + Lr (203-8)

D + (W or E/1.4) (203-9)

0.9 D ± E/1.4 (203-10)

D + 0.75 [L + Lr + (W or E/1.4)] (203-11)

Note: No increase in allowable stresses shall be used with these load combinations

Design of Buildings 2008

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