ASCE WIND LOAD EXAMPLES.pdf

WIND WEBINAR SERIES #3: ASCE 7 10 Wind Loads for Signs, Other Structures, Roof Top Structures & Equipment, and Other Special Conditions

Robert Paullus, P.E., S.E., SECB Paullus Structural Consultants [email protected]

26 February 2013 Wind Webinar #3 26 February 2013

Page 1 of 126

Wind Loads for Solid Signs, Other Structures, Roof-Top Structures & Equipment, and Other Special Conditions Bob Paullus, P.E., S.E. Paullus Structural Consultants

Wind Webinar #3 26 February 2013

Page 2 of 126

Outline 1. 1. Chapter 29– Other Structures (MWFRS Directional Method) a. b. c. d. e. f. g. h. i.


Conditions Limitations Solid Freestanding Walls or Signs Solid Attached Signs Design Wind Loads on Other Structures Design Wind Loads on Rooftop Structures and Equipment on Buildings Parapets Roof Overhangs Minimum Design Wind Loadings Page 3 of 126

Outline 1. 2. Chapter 30 – Part 6 - Components & Cladding for Building Appurtenances and Rooftop Structures and Equipment (Directional Procedure) a. b. c.

Parapets Roof Overhangs Rooftop Structures and Equipment for Buildings with h ≤ 60 ft (18.3 m)

2. 3. Examples


Page 4 of 126

Section 29.1.2 - Conditions • 1. The structure is a regular-shaped structure as defined in Section 26.2.2. •


Section 26.2.2 - BUILDING OR OTHER STRUCTURE, REGULAR-SHAPED: A building or other structure having no unusual geometrical irregularity in spatial form.

Page 5 of 126

Section 29.1.2 - Conditions • 2. The structure does not have response characteristics making it subject to acrosswind loading, vortex shedding, or instability due to galloping or flutter; or it does not have a site location for which channeling effects or buffeting in the wake of upwind obstructions warrant special consideration.


Page 6 of 126

Section 29.1.3 – Limitations • 1. This chapter DOES consider: load magnification effect caused by gusts in resonance with along-wind vibrations of flexible structures. • 2. This chapter DOES NOT consider: Unusual shapes or configurations that lead to effects listed in Section 29.1.2 – Conditions.


Page 7 of 126

Section 29.1.3 – Limitations • 3. If your structure does not fall within the listed limitations, it should probably be the subject of Wind Tunnel Study.


Page 8 of 126

Section 29.1.4 – Shielding • 1. No reductions allowed for apparent shielding by buildings, other structures, or terrain features. a. b. c.

Individual hills Individual trees or small groves of trees Individual levees and similar features.

• 2. Reductions are afforded for Terrain Features in determining Exposure Categories in Chapter 26. Wind Webinar #3 26 February 2013

Page 9 of 126

Steps


Page 10 of 126

Steps to Determine Wind Loads • 1. Steps 1-4 are the same as in Chapters 26-30. a. Chapter 29, like Chapters 26-30, has its own table, Table 29.3-1, for Kh and Kz b. Step 5: Eq. 29.3-1 qz = 0.00256KzKztKdV2 (lb/ft2)

• 2. Be careful to use qz or qh, as directed under each section.


Page 11 of 126

Section 29.4.1 – Solid Freestanding Walls and Solid Freestanding Signs • 1. Hollow Signs and Walls are not covered. a. Signs which have openings that can be pressurized 1) Boxed signs 2) Signs made from sea containers 3) Signs with large internal areas for lights with translucent panels

2. Research is being conducted at Texas Tech University by Douglas Smith, PhD


Page 12 of 126

Section 29.4.1 – Solid Freestanding Walls and Solid Freestanding Signs • 3. Solid Signs can have openings up to 30% of the Gross Area. a. Reduction factor can be applied to solid signs with openings. b. Reduction factor (1 - (1 - ε)1.5) c. ε = ratio of solid area to gross area

4. If the area of openings exceeds 30% of the gross area, it is an open sign. – Proceed to Section 29.5 - Design Wind

Loads—Other Structures


Page 13 of 126

Section 29.4.1 – Solid Freestanding Walls and Solid Freestanding Signs • 5. Basic Equation: (Eq. 29.4-1) F = qhGCfAs (lb) •


a. qh = the velocity pressure evaluated at height h (defined in Fig. 29.4-1) as determined in accordance with Section 29.3.2 » h = top of the wall or sign » Note: qh is at the top of the sign or wall and Kd in Eq 29.3-1 is the Kd of Solid Freestanding Walls and Solid Freestanding and Attached Signs in Table 26.6-1 Page 14 of 126

Section 29.4.1 – Solid Freestanding Walls and Solid Freestanding Signs •

b. G = gust-effect factor from Section 26.9 c. Cf = net force coefficient from Fig. 29.4-1 d. As = the gross area of the solid freestanding wall or freestanding solid sign, in ft2 (m2)


Page 15 of 126

Figure 29.4-1


Page 16 of 126

Figure 29.4-1


Page 17 of 126

Figure 29.4-1


Page 18 of 126

Section 29.4.1 – Solid Freestanding Walls and Solid Freestanding Signs • Load Cases to Consider • Case A – Load applied to the centroid of the area • Case B – Load applied with an eccentricity of 0.2*B (width of the wall or sign) • Case C – Stepped application of reduced wind pressures as the distance decreases from the windward edge.


Page 19 of 126

Section 29.4.1 – Solid Freestanding Walls and Solid Freestanding Signs •

Case C – Reduction in loads for walls or signs with

returns at the ends » Up to 40 % reduction – For Elevated Signs or walls: where s/h > 0.8, force coefficients shall be multiplied by the reduction factor (1.8 - s/h) » Accounts for reduced wind pressures when free air flow under the wall or sign is reduced.


Page 20 of 126

Section 29.4.1 – Solid Freestanding Walls and Solid Freestanding Signs


Page 21 of 126

Section 29.4.1 2 - Solid Attached Signs a.1. Requirements to use method in Section 29.4.1 a.

b.

c.

d.


The plane of the sign is parallel to and in contact with the supporting wall Edges of the sign do not extend past the supporting wall Use Component & Cladding Wall pressures calculated in Chapter 30 Set the Internal Pressure Coefficient (GCpi) equal to 0

Page 22 of 126

Section 29.4.1 2 - Solid Attached Signs a. 2.

Procedure can also be used for signs attached to but not in contact with the supporting wall. a. b.

c.

Sign must be parallel to the supporting wall. Sign must not be more than three (3) feet from the wall. Edges of the sign must be at least (3) feet in from the free edges of the supporting wall: b.

Top of the supporting wall. Bottom of the supporting wall

c.

Side Edges of the supporting wall

a.


Page 23 of 126

Section 29.5: Design Wind Loads—Other Structures


Page 24 of 126

Section 29.5: Design Wind Loads—Other Structures Basic Equation: (Eq. 29.5-1) F = qzGCfAf (lb) (N) a. qz = velocity pressure evaluated at height z as defined in Section 29.3, of the centroid of area Af » Note qz is at the centroid of the area and Kd in Eq 29.3-1 is the Kd of the structure type in Table 26.6-1 b. G = gust-effect factor from Section 26.9 (these structures may often be flexible) c. Cf = force coefficients from Figs. 29.5-1


Page 25 of 126

Section 29.5: Design Wind Loads—Other Structures d. Af = projected area normal to the wind except where Cf is specified for the actual surface area, in ft2 (m2)


Page 26 of 126

Figure 29.5-1


Page 27 of 126

Figure 29.5-1


Page 28 of 126

Figure 29.5-2


Page 29 of 126

Figure 29.5-2


Page 30 of 126

Figure 29.5-3


Page 31 of 126

Figure 29.5-3


Page 32 of 126

Section 29.5-1 – Rooftop Structures and Equipment For Buildings with h ≤ 60 feet 1. No guidance is given for rooftop

structures on buildings > 60 feet. 2. Research in the ASCE 7 committee suggests that it is probably acceptable to use loads from this section for rooftop structures on buildings > 60 feet, but this has not been confirmed yet. 3. Equation 29.5-2 gives lateral pressure on the rooftop structure. Wind Webinar #3 26 February 2013

Page 33 of 126

Section 29.5-1 – Rooftop Structures and Equipment For Buildings with h ≤ 60 feet Lateral Wind force on Rooftop Structures

• –


Basic Equation: (Eq 29.5-2) Fh = qh(GCr)Af (lb) (N) » (GCr) = 1.9 for rooftop structures and equipment with Af less than (0.1Bh). (GCr) shall be permitted to be reduced linearly from 1.9 to 1.0 as the value of Af is increased from (0.1Bh) to (Bh). » qh = velocity pressure evaluated at mean roof height of the building

Page 34 of 126

Section 29.5-1 – Rooftop Structures and Equipment For Buildings with h ≤ 60 feet •

Lateral Wind force on Rooftop Structures »

»


Note, qh is at the mean roof height and Kd in Eq 29.3-1 is the Kd of the building, in Table 26.6-1, on which the rooftop structure sits. Af = vertical projected area of the rooftop structure or equipment on a plane normal to the direction of wind, in ft2 (m2)

Page 35 of 126

Section 29.5-1 – Rooftop Structures and Equipment For Buildings with h ≤ 60 feet Vertical Wind force on Rooftop Structures

• –


Basic Equation: (Eq 29.5-3) Fv = qh(GCr)Ar (lb) (N) » (GCr) = 1.5 for rooftop structures and equipment with Ar less than (0.1BL). (GCr) shall be permitted to be reduced linearly from 1.5 to 1.0 as the value of Ar is increased from (0.1BL) to (BL). » qh = velocity pressure evaluated at mean roof height of the building

Page 36 of 126

Section 29.5-1 – Rooftop Structures and Equipment For Buildings with h ≤ 60 feet •

Vertical Wind force on Rooftop Structures »

»


Note qh is at the mean roof height and Kd in Eq 29.3-1 is the Kd of the building, in Table 26.6-1, on which the rooftop structure sits. Ar = horizontal projected area of rooftop structure or equipment, in ft2 (m2)

Page 37 of 126

Section 30.11 – Component & Cladding Loads for Rooftop Structures and Equipment for Buildings with h ≤ 60 feet Lateral C & C pressure (psf) shall be equal to the lateral force (Lbs) calculated with equation (29.5-2) DIVIDED BY the RESPECTIVE WALL Surface area of the Rooftop Structure considered.

•

–


Forces (psf) shall be considered to act inward and outward

Page 38 of 126

Section 30.11 – Component & Cladding Loads for Rooftop Structures and Equipment for Buildings with h ≤ 60 feet Vertical C & C pressure (Lbs) shall be equal to the vertical force (Lbs) calculated with equation (29.5-3) DIVIDED BY the Horizontal projected area of the roof of the Rooftop Structure considered.

•

–


The pressures are ONLY required to be considered to act in the UPWARD direction.

Page 39 of 126

Section 30.11 – Component & Cladding Loads for Rooftop Structures and Equipment for Buildings with h ≤ 60 feet Comment: If the Rooftop Structure is large (10’x20’ or larger), consider looking at the downward pressures from the building C&C loading figures and make some judgment about downward wind loading rooftop structures that resemble small buildings (penthouses for instance).

•

– – Wind Webinar #3 26 February 2013

Vertical Wind Load would act in addition to Dead and Roof Live Loads or Snow Loads. Use appropriate load combinations. Page 40 of 126

Other Resources


Page 41 of 126

Other Resources • Prepared by: Task Committee on WindInduced Forces of the Petrochemical Committee of the Enginery Division of ASCE • Several of those on the Task Committee are on the ASCE 7 Wind Subcommittee • Based on ASCE 7-05


Page 42 of 126

Section 29.6 – Parapets (MWFRS) •

•


“Wind loads on parapets are specified in Section 27.4.5 for buildings of all heights designed using the Directional Procedure and in Section 28.4.2 for low-rise buildings designed using the Envelope Procedure.” Method presented is the Directional Procedure

Page 43 of 126

Section 29.6 – Parapets (MWFRS) Chapter 28 – The Envelope Method, is exactly the same.

• –


Chapter 28 uses the velocity pressure determined with the Envelope Method, rather than the velocity pressure in Chapter 27 using the Directional Method.

Page 44 of 126

Section 27.4.5 - Parapets MWFRS pressures due to parapets

•


–

Rigid or Flexible Buildings

–

Applies to Flat, Gable, or Hip Roofs

Page 45 of 126

Section 27.4.5 – Parapets (MWFRS) Basic Equation: (Eq 27.4-4) pp = qp(GCpn) (lb/ft2)

• –


pp = combined net pressure on the parapet due to the combination of the net pressures from the front and back parapet surfaces. Plus (and minus) signs signify net pressure acting toward (and away from) the front (exterior) side of the parapet

Page 46 of 126

Section 27.4.5 – Parapets (MWFRS) –


qp = velocity pressure evaluated at the top of the parapet » (GCpn) = combined net pressure coefficient – = +1.5 for windward parapet – = –1.0 for leeward parapet

Page 47 of 126

Section 27.4.5 – Parapets (MWFRS) • FIGURE C29.7-1 Design Wind Pressures on Parapets


Page 48 of 126

Section 30.9 – C & C Loading on Parapets • •


Applicable to All Building Types Applicable to All Building Heights – Except Where the Provisions of Part 4 are used (Simplified Method for Buildings with h ≤ 160 feet)

Page 49 of 126

Section 30.9 – C & C Loading on Parapets Basic Equation: (Eq. 30.9-1) p = qp((GCp) – (GCpi))

• – –


qp = velocity pressure evaluated at the top of the parapet (GCp) = external pressure coefficient given in » Fig. 30.4-1 for walls with h ≤ 60 ft (48.8 m) » Figs. 30.4-2A to 30.4-2C for flat roofs, gable roofs, and hip roofs » Fig. 30.4-3 for stepped roofs

Page 50 of 126

Section 30.9 – C & C Loading on Parapets –


(GCp) = external pressure coefficient given in » Fig. 30.4-4 for multispan gable roofs » Figs. 30.4-5A and 30-5B for monoslope roofs » Fig. 30.4-6 for sawtooth roofs » Fig. 30.4-7 for domed roofs of all heights » Fig. 30.6-1 for walls and flat roofs with h > 60 ft (18.3 m) » Fig. 27.4-3 footnote 4 for arched roofs

Page 51 of 126

Section 30.9 – C & C Loading on Parapets –

Consider Two (2) Load Cases when evaluating C & C pressures on parapets

• – –


(GCpi) = internal pressure coefficient from Table 26.11-1, based on the porosity of the parapet envelope.

Case A – Pressures on the surfaces of the Windward parapet Case B – Pressures on the surfaces of the Leeward parapet

Page 52 of 126

Section 30.9 – C & C Loading on Parapets Specifics of Case A:

• –


Windward Parapet shall consist of applying the applicable positive wall pressure from Fig. 30.4-1 (h ≤ 60 ft (18.3 m)) or Fig. 30.6-1 (h > 60 ft (18.3 m)) to the windward surface of the parapet while applying the applicable negative edge or corner zone roof pressure from Figs. 30.4-2 (A, B or C), 30.4-3, 30.4-4, 30.4-5 (A or B), 30.4-6, 30.4-7, Fig. 27.4-3 footnote 4, or Fig. 30.6-1 (h > 60 ft (18.3 m)) as applicable to the leeward surface of the parapet.

Page 53 of 126

Section 30.9 – C & C Loading on Parapets Specifics of Case B:

• –


Leeward Parapet shall consist of applying the applicable positive wall pressure from Fig. 30.4-1 (h ≤ 60 ft (18.3 m)) or Fig. 30.6-1 (h > 60 ft (18.3 m)) to the windward surface of the parapet, and applying the applicable negative wall pressure from Fig. 30.4-1 (h ≤ 60 ft (18.3 m)) or Fig. 30.6-1 (h > 60 ft (18.3 m)) as applicable to the leeward surface. Edge and corner zones shall be arranged as shown in the applicable figures. (GCp)

Page 54 of 126

Section 30.9 – C & C Loading on Parapets • FIGURE C29.7-1 Design Wind Pressures on Parapets

•


If internal pressure is present, both load cases should be evaluated under positive and negative internal pressure.

Page 55 of 126

Table 30.9-1 – Steps to Determine C&C Wind Loads on Parapets


•

Step 1: Determine risk category of building, see Table 1.5-1

•

Step 2: Determine the basic wind speed, V, for applicable risk category, see Figure 26.51A, B or C

Page 56 of 126

Table 30.9-1 – Steps to Determine C&C Wind Loads on Parapets •

Step 3: Determine wind load parameters: – Wind directionality factor, Kd , see Section 26.6

and Table 26.6-1 » –

Use Kd for Buildings C&C (0.85)

Exposure category B, C or D, see Section 26.7

– Topographic factor, Kzt, see Section 26.8 and Fig.

26.8-1 – Enclosure classification, see Section 26.10 – Internal pressure coefficient, (GCpi), see Section 26.11 and Table 26.11-1 »


Open, Partially Enclosed, or Enclosed (parapet or bldg)

Page 57 of 126

Table 30.9-1 – Steps to Determine C&C Wind Loads on Parapets


•

Step 4: Determine velocity pressure exposure coefficient, Kh, at top of the parapet see Table 30.3-1

•

Step 5: Determine velocity pressure, qp, at the top of the parapet using Eq. 30.3-1

Page 58 of 126


Step 6: Determine external pressure coefficient for wall and roof surfaces adjacent to parapet, (GCp) – Walls with h ≤ 60 ft., see Fig. 30.4-1 – Flat, gable and hip roofs, see Figs. 30.4-2A to

30.4-2C – Stepped roofs, see Fig. 30.4-3 – Multispan gable roofs, see Fig. 30.4-4 – Monoslope roofs, see Figs. 30.4-5A and 30.4-5B – Sawtooth roofs, see Fig. 30.4-6


Page 59 of 126


Step 6: (Continued) – Domed roofs of all heights, see Fig. 30.4-7 – Walls and flat roofs with h > 60 ft., see Fig. 30.6-1 – Arched roofs, see footnote 4 of Fig. 27.4-3

•


Step 7: Calculate wind pressure, p, using Eq. 30.9-1 on windward and leeward face of parapet, considering two load cases (Case A and Case B) as shown in Fig. 30.9-1.

Page 60 of 126

Section 30.9 – C & C Loading on Parapets


Page 61 of 126

Figure 30.6-1

•

Note 7 defines parapets > 3 feet as tall parapets • •


Reduced corner pressures on parapet Similar note on other figures

Page 62 of 126

Section 29.7 – Roof Overhangs (MWFRS) “Wind loads on roof overhangs are specified in Section 27.4.4 for buildings of all heights designed using the Directional Procedure and in Section 28.4.3 for lowrise buildings designed using the Envelope Procedure.” • Present Direction Method in Section 27.4.1 •

– Envelope Method in Section 28.3.1 is similar – Uses different factor for Cp


Page 63 of 126

Section 27.4 – Roof Overhangs (MWFRS) •


The positive external pressure on the bottom surface of windward roof overhangs shall be determined using Cp = 0.8 and combined with the top surface pressures determined using Fig. 27.4-1.

Page 64 of 126

Section 27.4 – Roof Overhangs (MWFRS)


Page 65 of 126

Section 27.4 – Roof Overhangs (MWFRS)


•

From Figure 27.6-3

•

Must consider cases with positive internal pressure and negative internal pressure

Page 66 of 126

Section 30.10 – C & C Loading on Roof Overhangs • •


Applicable to All Building Types Applicable to All Building Heights – Except Where the Provisions of Part 4 are used (Simplified Method for Buildings with h ≤ 160 feet)

Page 67 of 126

Section 30.10 – C & C Loading on Roof Overhangs Basic Equation: (Eq. 30.10-1) p = qh((GCp) – (GCpi))

• –

–


qh = velocity pressure from Section 30.3.2 evaluated at mean roof height h using exposure defined in Section 26.7.3 (GCp) = external pressure coefficients for overhangs given in Figs. 30.4-2A to 30.4-2C (flat roofs, gable roofs, and hip roofs), including contributions from top and bottom surfaces of overhang.

Page 68 of 126

Section 30.10 – C & C Loading on Roof Overhangs »

–


The external pressure coefficient for the covering on the underside of the roof overhang is the same as the external pressure coefficient on the adjacent wall surface, adjusted for effective wind area, determined from Figure 30.4-1 or Figure 30.6-1 as applicable

(GCpi) = internal pressure coefficient given in Table 26.11-1

Page 69 of 126

Figure 30.4-2A


Page 70 of 126

Figure 30.4-1


Page 71 of 126

Table 30.10-1 – Steps to Determine C&C Wind Loads on Roof Overhangs


•

Step 1: Determine risk category of building, see Table 1.5-1

•

Step 2: Determine the basic wind speed, V, for applicable risk category, see Figure 26.51A, B or C

Page 72 of 126

Table 30.10-1 – Steps to Determine C&C Wind Loads on Roof Overhangs •

Step 3: Determine wind load parameters: – Wind directionality factor, Kd , see Section 26.6

and Table 26.6-1 » –

Use Kd for Buildings C&C (0.85)

Exposure category B, C or D, see Section 26.7

– Topographic factor, Kzt, see Section 26.8 and Fig.

26.8-1 – Enclosure classification, see Section 26.10 – Internal pressure coefficient, (GCpi), see Section 26.11 and Table 26.11-1 »


Open, Partially Enclosed, or Enclosed (overhang or bldg)

Page 73 of 126



•

Step 4: Determine velocity pressure exposure coefficient, Kh, see Table 30.3-1

•

Step 5: Determine velocity pressure, qh, at mean roof height h using Eq. 30.3-1

Page 74 of 126



•

Step 6: Determine external pressure coefficient, (GCp), using Figs. 30.4-2A through C for flat, gabled and hip roofs.

•

Step 7: Calculate wind pressure, p, using Eq. 30.10-1. Refer to Figure 30.10-1

Page 75 of 126

Figure 30.10-1


Page 76 of 126

Section 29.8 – Minimum Design Wind Loading (MWFRS) •

The design wind force for other structures shall be not less than 16 lb/ft2 (0.77 kN/m2) multiplied by the area Af. – 16 psf is 10 psf from ASCE 7-05 times 1.6 to bring

the load to a strength level load. – Apply to the full projected area in each orthogonal direction.


Page 77 of 126

Material in Chapters 29 Not Covered Loads on many shapes in industrial plants – Tanks, Silos, Pipe racks, Partially Clad Frames, etc. – See ASCE report: “Wind Loads for Petrochemical and Other Industrial Facilities” • Wind Loads on roof mounted Solar Photovoltaic Arrays – See new SEOC Guide •


Page 78 of 126

Other Ressources


Page 79 of 126

Example • Office Complex • Location: Wichita, KS • Freestanding Sign • 3-Story Office – 5-foot tall parapet – Roof Top Unit • Well Pump & Maintenance Building – Roof Overhang • Chemical Storage Silo Wind Webinar #3 26 February 2013

Page 80 of 126

Example • Site Parameters Common to All Examples •

Exposure (Terrain Roughness): C Location: N 37.7500, W 97.1683 – Section 26.7.3 (Open Farmland) –

•

Risk Category II Structures –

•

Table 1.5-1

Wind Velocity: 115 mph Fig. 26.5-1A – http://www.atcouncil.org/windspeed/index.php –

•

Topographic Factor, Kzt: 1.00 –

•


Section 26.8

All Loads are Calculated to LRFD Levels Page 81 of 126

Example


Page 82 of 126

Example-Freestanding Sign • Solid Billboard Sign at Ground Level • •

• • • • • •


Dimensions: 30’ Wide x 10’ High Reference Figure 29.4-1 (MWFRS) – s=10’ – B=30’ – h=10’ Kh = 0.85 (Table 29.3-1) Kd = 0.85 (Solid Freestanding Walls & Signs)(Table 26.6-1) qh = 0.00256 KzKztKdV2 (psf) qh = 0.00256(0.85)(1.00)(0.85)(115)2 = 24.46 psf B/s = 30’/10’ = 3.0 s/h = 10’/10’ = 1.0

Page 83 of 126

Example-Freestanding Sign •

Enter Figure 29.4-1 for Cf – Applies to Cases A & B For B/s = 2: Cf = 1.40 – For B/s = 4: Cf = 1.35 – Interpolating for B/s 3.0, Cf = 1.375 G = 0.85 (Section 26.9 – Rigid Structure) F = qhGCfAs (Lb) (Eq 29.4-1) F = (24.46 psf)(0.85)(1.375)As = 28.59 psf*As – As = Af = 30’x10’ = 300 ft2 – 28.59 psf*As > 16 psf * Af (Section 29.8 Min. Load) F = 28.59 psf(300 ft2) = 8577 Lbs – For CASE A, Load is applied at the plan C.L. and at – (s/2)+(0.05h) = 5.5’ above base –

• • •

•


Page 84 of 126

Example-Freestanding Sign See Cross-Section View, Figure 29.4-1 – For CASE B, Load is applied @ 5.5’ above base and at 0.2B offset, either side of plan C.L. » 0.2B = 0.2(30’) = 6.0’ either side of plan C.L. Check to see if CASE C must be considered – Note 3, Figure 29.4-1 – If B/s ≥ 2.0, CASE C must be considered – B/s = 30’/10’ = 3.0 > 2.0, therefore consider CASE C Enter Figure 29.4-1 for Cf, under CASE C – 0-s (0’-10’): Cf = 2.60 – s-2s (10’-20’): Cf = 1.70 – 2s-3s (10’-30’): Cf = 1.15 »

•

•


Page 85 of 126

Example-Freestanding Sign For CASE C, where s/h > 0.8, Cf may be multiplied by the reduction factor (1.8 – s/h) – s/h = 1.0 > 0.8 – (1.8 – s/h) = (1.8 – 1.0) = 0.8 – F = qhGCfAs (Lb) (Eq 29.4-1) – F1 = (24.46psf)(0.85)(2.60)(0.8)(10’x10’) = 4324 Lbs – F2 = (24.46psf)(0.85)(1.70)(0.8)(10’x10’) = 2828 Lbs – F3 = (24.46psf)(0.85)(1.15)(0.8)(10’x10’) = 1913 Lbs » Apply F1, F2, and F3 at plan C.L. of each plan length, s, from each end of sign. See Figure. » Apply F1, F2 and F3 at 5.5’ above base of each plan length, s –


Page 86 of 126

Example-Freestanding Sign


Page 87 of 126

Example-Parapet (MWFRS) • Parapet (MWFRS) (Section 29.6) • Office Building – L = 200 ft., B = 100 ft. – Roof Height: h = 40 ft. – Parapet Height: hp = 45 ft. – Roof Slope, Flat: 0.25:12 » Ridge parallel to 200’ side – Exposure Category: C •


Section 29.6 references Section 27.4.5 for directional procedure for MWFRS Parapet load determination.

Page 88 of 126

Example-Parapet (MWFRS) pp = qp(GCpn) (psf) – qp = 0.00256KhKztKdV2 (psf) (Eq 27.3-1) – Kh @ hp = 45’, Kh = 1.065 – Kzt = 1.00 (for complex) – Kd = 0.85 (Building MWFRS)(Table 26.6-1) – V = 115 mph (for complex) – qp = 0.00256(1.065)(1.00)(0.85)(115)2 = 30.65 psf – GCpn = +1.5 for windward parapet (Section 27.4.5) – GCpn = -1.0 for leeward parapet (Section 27.4.5) Windward Parapet – pp = (30.65 psf)(1.5) = 45.98 psf acting toward building Leeward Parapet – pp = (30.65 psf)(-1.0) = -30.65 psf acting away from building –

• •


Page 89 of 126

Example-Parapet (C & C) • Parapet (C & C Loads) (Section 30.9) •

Office Building – same as previous

•

qp = 0.00256(1.065)(1.00)(0.85)(115)2 = 30.65 psf – from parapet MWFRS, above p = qp((GCp) – (GCpi)) (Eq 30.9-1) Parapet can be pressurized along with building – See Figure GCpi = ± 0.18 (Enclosed Building – Table 26.11-1)

• •

•


Page 90 of 126

Example-Parapet (C & C)


Page 91 of 126

Example-Parapet (C & C) • •

•


Studs @ 16” o.c. (both faces) Determine Effective Wind Area of Studs – Greater of Tributary Area or Effective Width » Effective Wind Area Definition (Section 26.2) – Greater of 16”/12” = 1.33’ or – Length/3 = 5’/3 = 1.67’ (governs) » Effective Wind Area: l2/3 = 52/3 = 8.33 ft2 » If Effective Wind Area > 700 ft2, use MFWRS loads Determine which figure to reference from Table 30.9-1, Step 6 – Figure 30.4-1 for wall pressures, h ≤ 60 ft.

Page 92 of 126

Example-Parapet (C & C) Figure 30.4-2A for roof loads, h ≤ 60 ft. and gable roofs θ ≤ 7° ° – Determine “a” distance (Figure 30.4-1 and 30.4-2A) » Lesser of 10% of B = 0.10(100’) = 10’ and 0.4h = 0.4(40’) = 16’ – 10’ governs » Not less than the greater of 4% of B = 0.04(100’) = 4’ or 3’ » a = 10’ – Entering Figure 30.4-1 for pressure coefficients on exterior surfaces of the parapets: » Zone 4 Positive Pressure: GCp = 1.0 » Zone 5 Positive Pressure: GCp = 1.0

–


Page 93 of 126

Example-Parapet (C & C) Zone 4 Negative Pressure: GCp = -1.1 » Zone 5 Negative Pressure: GCp = -1.4 – Note 5 says that values of GCp may be reduced by 10% when θ ≤ 10° ° » Zone 4 Positive Pressure: GCp = (0.9)1.0 = 0.9 » Zone 5 Positive Pressure: GCp = (0.9)1.0 = 0.9 Zone 4 Negative Pressure: GCp = (0.9)-1.1 = -1.0 » Zone 5 Negative Pressure: GCp = (0.9)-1.4 = -1.26 – Entering Figure 30.4-2A for pressure coefficients on interior (roof side) surfaces of parapet: » Effective Wind Area: A= 52/3 = 8.33 ft2 » a = 10 ft. as in Figure 30.4-1 » Zone 1, 2, and 3 Positive Pressure: GCp = 0.3 »


Page 94 of 126

Example-Parapet (C & C) » » »

»


Zone 1 Negative Pressure: GCp = -1.0 Zone 2 Negative Pressure: GCp = -1.8 Zone 3 Negative Pressure: GCp = -2.8 – Note 5: “If a parapet equal to or higher than 3 ft (0.9m) is provided around the perimeter of the roof with θ ≤ 7° °, the negative values of GCp in Zone 3 shall be equal to those for Zone 2 and positive values of GCp in Zones 2 and 3 shall be set equal to those for wall Zones 4 and 5 respectively in Figure 30.4-1.” Parapet height hp = 5’ > 3’ – Zone 3 Negative GCp is Not Applicable – Zone 2 and Zone 3 Positive Pressure GCp are those of Wall Zone 4 and Zone 5, respectively.

Page 95 of 126

Example-Parapet (C & C) •

•


Step 7: Calculate wind pressure, p using Eq 30.9-1 on windward and leeward faces of parapet, considering two load cases (CASE A and CASE B) as shown in Figure 30.9-1 – Note: As wind direction changes, each parapet with shift from a windward parapet to a leeward parapet. CASE A – Windward Parapet – Exterior Face Wall Studs » p = qp((GCp) – (GCpi)) (Eq 30.9-1) » With Positive Internal Pressure – Zone 4 = Zone 5 – P = (30.65 psf)((0.9)-(0.18)) = 22.06 psf » With Negative Internal Pressure – Zone 4 = Zone 5 – p = (30.65 psf)((0.9)-(-0.18)) = 33.10 psf

Page 96 of 126

Example-Parapet (C & C) Apply to Tributary Area, not Effective Wind Area – 33.10 psf(1.33’) = 44.12 plf – Interior Face (roof side) Parapet Studs » p = qp((GCp) – (GCpi)) (Eq 30.9-1) » With Positive Internal Pressure – Zone 2 (Zone 3 also treated as Zone 2) – p = (30.65 psf)((-1.8)-(0.18)) = -60.69 psf » With Negative Internal Pressure – Zone 2 (Zone 3 also treated as Zone 2) – p = (30.65 psf)((-1.8)-(-0.18)) = -40.65 psf » Apply to Tributary Area, not Effective Wind Area – -60.69 psf(1.33’) = -80.72 plf »


Page 97 of 126

Example-Parapet (C & C) •


CASE B – Leeward Parapet – Interior Face Parapet Studs (load toward parapet) » p = qp((GCp) – (GCpi)) (Eq 30.9-1) » With Positive Internal Pressure – Substitute Zone 4 and Zone 5 pressures for roof Zone 2 and Zone 3 pressures, respectively. Zone 4 = Zone 5 – P = (30.65 psf)((0.9)-(0.18)) = 22.06 psf » With Negative Internal Pressure – Zone 4 = Zone 5 – p = (30.65 psf)((0.9)-(-0.18)) = 33.10 psf » Apply to Tributary Area, not Effective Wind Area – 33.10 psf(1.33’) = 44.12 plf

Page 98 of 126

Example-Parapet (C & C) –


Exterior Face Wall Studs (load away from parapet) » p = qp((GCp) – (GCpi)) (Eq 30.9-1) » With Positive Internal Pressure – Zone 4 pressure – p = (30.65 psf)((-1.0)-(0.18)) = -36.17 psf – Zone 5 pressure – p = (30.65 psf)((-1.26)-(0.18)) = -44.14 psf » With Negative Internal Pressure – Zone 4 pressure – p = (30.65 psf)((-1.0)-(-0.18)) = -25.13 psf – Zone 5 pressure – p = (30.65 psf)((-1.26)-(-0.18)) = -33.10 psf

Page 99 of 126

Example-Parapet (C & C) Apply to Tributary Area, not Effective Wind Area – Zone 4 – -36.17 psf(1.33’) = -48.11 plf – Zone 5 – -44.14 psf(1.33’) = -58.71 plf – Summary » Exterior Wall Studs extended past roof into parapet: – Zone 4: 44.12 plf (toward building) – Zone 4: -48.11 plf (away from building) – Zone 5 is anything within 10ft of the corner – Zone 5: 44.12 plf (toward building) – Zone 5: -58.71 plf (away from building) »


Page 100 of 126

Example-Parapet (C & C) »


Interior (roof side) Parapet Studs – Zone 4: 44.13 plf (toward parapet) – Zone 4: -80.72 plf (away from parapet) – Zone 5 is anything within 10ft of the corner – Zone 5: 44.13 plf (toward parapet) – Zone 5: -80.92 plf (away from parapet)

Page 101 of 126

Example-Rooftop Equip. (MWFRS) • Rooftop Equipment for Buildings (MWFRS) (Section 29.5.1) • • • • • • • • •


Office Building – same as previous Plan Dimensions: 10’ wide x 20’ long RTU Height: 4’ over 1’ tall curb Projected Height: 4’+1’=5’ Lateral Force: Fh = qh(GCr)Af (Lb) (Eq 29.5-2) Vertical Force: Fv = qh(GCr)Ar (Lb) (Eq 29.5-3) qh calculated at mean roof height of building Kh @ h = 40’, Kh = 1.04 (Table 29.3-1) Use Kd for building NOT Kd for rectangular Other Structures

Page 102 of 126

Example-Rooftop Equip. (MWFRS) • • • •


Kd = 0.85 (Table 26.6-1) Other parameters as previously defined for building qh = 0.00256(1.04)(1.00)(0.85)(115)2 = 29.93 psf HORIZONTAL WIND FORCE – Check projected area of side compared with least projected area of building » B*h = 100’(40’) = 8000 ft2 » Af (max) = 20’(5’) = 100 ft2 » Af <0.1Bh: 100 ft2 < 800 ft2 – GCr = 1.9 – Fh = (29.93 psf)(1.9)(Af) = 56.87 psf(Af) < 16 psf(Af) » Minimum Load from Section 29.8 – Fh = (29.93 psf)(1.9)(100 ft2) = 5687Lbs(Eq 29.5-2)

Page 103 of 126

Example-Rooftop Equip. (MWFRS) Perpendicular to long side – Fh = (29.93 psf)(1.9)(50 ft2) = 2843 Lbs (Eq 29.5-2) » Parallel to long side – Horizontal wind forces applied to geometric center of vertical projected plane of unit VERTICAL WIND FORCE – Check projected area of roof compared with that of building » B*L = 100’(200’) = 20,000 ft2 » Ar = 20’(10’) = 200 ft2 » Ar <0.1BL: 200 ft2 < 2,000 ft2 – GCr = 1.5 – Fv = (29.93 psf)(1.5)(200 ft2) = 8979Lbs(Eq 29.5-2) »

•


Page 104 of 126

Example-Rooftop Equip. (MWFRS) Vertical Up – Vertical wind forces applied to geometric center of horizontal projected plane of unit Note: The UPLIFT pressure on the top of the rooftop equipment acts SIMULTANEOUSLY with either the Lateral pressure parallel to or perpendicular to the long edge of the rooftop equipment or structure. The same procedure is used for a roof-mounted penthouse. »

•

•


Page 105 of 126

Example-Rooftop Equip. (C & C) • Rooftop Equipment for Buildings (C&C) (Section 30.11) • • • •

•


Loads for Designing the Equipment cabinet enclosure or the wall components for a penthouse Lateral C & C pressures Fh = 5687 Lbs (from previous) C & C Lateral Loads: Fh/Af = 5687 Lbs/100 ft2 = 56.87 psf – Load is applied toward or away from unit on all sides C & C Vertical Loads: Fv/Ar = 8979 Lbs/200 ft2 = 44.90 psf – Load is applied only in the Upward direction, away from the top of the unit

Page 106 of 126

Example-Rooftop Equip. (C & C) •


Personal Recommendation (Not in the Standard) – If the unit is large (over 200 ft2), consider a minimum downward wind load. – C & C Loading from Figure 30.4-2A » GCp = 0.2 (downward component) » Fv = qhGCp = (29.93psf)(0.2) = 6 psf » For higher wind loads and low snow loads, particularly less than 10 psf, this may produce a controlling load combination

Page 107 of 126

Example-Roof Overhang (MWFRS) • Roof Overhang (MWFRS) (Section 29.7) • Equipment Building – L = 60 ft., B = 30 ft. – Eave Height: 10 ft. – Overhang Width: 3 ft. – Roof Slope: 4.375:12 (θ = 20° °) » Ridge parallel to 60’ side – Exposure Category: C – Average Building Height: h = 13.28’ < 15’ •


Section 29.7 references Section 27.4.4 for directional procedure for MWFRS Roof Overhang load determination. Page 108 of 126

Example-Roof Overhang (MWFRS) Use Cp = 0.8 in Eq 27.4-1 for determining roof and wall loads over and adjacent to roof overhang – p = qGCp-qi(GCpi) (psf) (Eq 27.4-1) – G = 0.85 (rigid structure) (Section 26.9) – Kzt = 1.00 (for complex) – Kd = 0.85 (Building MWFRS)(Table 26.6-1) – V = 115 mph (for complex) – Kz @ z = 10’ for soffit, Kz = 0.85 (Table 27.3-1) – qz = 0.00256KzKztKdV2 (psf) (Eq 27.3-1) – qz = 0.00256(0.85)(1.00)(0.85)(115)2 = 24.46 psf – GCpi = ± 0.18 (Enclosed building)(Figure 26.11-1) – Transverse Wind Loading governs, by Inspection –


Page 109 of 126

Example-Roof Overhang (MWFRS) Pressure on underside of roof overhang » p = (24.46 psf)(0.85)(0.8) – (24.46 psf)(0.18) » p = 12.23 psf (positive internal pressure) » p = (24.46 psf)(0.85)(0.8) – (24.46 psf)(-0.18) » p = 21.04 psf (negative internal pressure) – Enter Figure 27.4-1 for pressures on windward roof » h/L = 13.28’/60’ = 0.22 < 0.25 » Cp = 0.2 (Condition 1) » Cp = -0.3 (Condition 2) » Condition 1 – p = (24.46 psf)(0.85)(0.2) – (24.46 psf)(0.18) – p = 0.24 psf (positive internal pressure) – p = (24.46 psf)(0.85)(0.2) – (24.46 psf)(-0.18) – p = 8.56 psf (negative internal pressure) –


Page 110 of 126

Example-Roof Overhang (MWFRS) »

»


Condition 2 – p = (24.46 psf)(0.85)(-0.3) – (24.46 psf)(0.18) – p = -10.64 psf (positive internal pressure) – p = (24.46 psf)(0.85)(-0.3) –(24.46 psf)(-0.18) – p = -1.83 psf (negative internal pressure) Combine Top & Bottom Pressures with Same Internal Pressure Conditions – Note: signs indicate pressure toward or away from surface – Change signs so (+) is up, globally – Change signs so (-) is down, globally

Page 111 of 126

Example-Roof Overhang (MWFRS) –

–

–


Positive Internal Pressure – povh = 12.23 psf - 0.24 psf = 11.99 psf – povh = 12.23 psf + 10.64 psf = 22.87 psf – overall povh is upward Negative Internal Pressure – povh = 21.04 psf – 8.56 psf = 12.48 psf – povh = 21.04 psf + 1.83 psf = 22.87 psf – overall povh is upward Note: Net effect of internal pressures is zero so that the total uplift on the overhang is the same.

Page 112 of 126

Example-Roof Overhang (MWFRS) –


Overall pressure on the Leeward Overhang is calculated the same way, but uses the negative pressure on the wall immediately adjacent to the overhang for downward pressures on soffit. – By inspection, total force on windward overhang will control.

Page 113 of 126

Example-Roof Overhang


Page 114 of 126

Example-Roof Overhang (C & C) • Roof Overhang (C & C) (Section 30.10) •

•


Equipment Building – Unless otherwise listed, parameters are identical to those for the MWFRS calculations – Determine C & C loads for overhangs of roof trusses, spaced at 2’-0” o.c. p = qh[(GCp) – (GCpi)] psf (Eq 30.10-1) – Kd = 0.85 (Building C&C) (Table 26.6-1) – All other parameters for qh are same as for MFWRS

Page 115 of 126

Example-Roof Overhang (C & C) qh = 0.00256(0.85)(1.00)(0.85)(115)2 = 24.46 psf Enter Figure 30.4-2B for Roof Overhang C & C coefficients Determine Effective Wind Area of Studs – Greater of Tributary Area or Effective Width » Effective Wind Area Definition (Section 26.2) – Greater of 2.0’ or (governs) – Length/3 = 3’/3 = 1.00’ » Effective Wind Area: 3’x2’ = 6.00 ft2 » If Effective Wind Area > 700 ft2, use MFWRS loads – Determine “a” distance (Figure 30.4-1 and 30.4-2A) » Lesser of 10% of B = 0.10(30’) = 3’ and 0.4h = 0.4(13.28’) = 5.31’ – 3’ governs –

• •


Page 116 of 126

Example-Roof Overhang (C & C) Not less than the greater of 4% of B = 0.04(30’) = 1.2’ or 3’ (3’ controls) » a = 3’ (equal to width of overhang; therefore, Zone 1 pressures are not applicable to any part of the overhang) – Zone 2: GCp = -2.2 » p = (24.46 psf)[(-2.2) – (0.18)] = -58.21 psf – with positive internal building pressure » p = (24.46 psf)[(-2.2) – (-0.18)] = -49.41 psf – with negative internal building pressure – Zone 3: GCp = -3.7 » p = (24.46 psf)[(-3.7) – (0.18)] = -94.90 psf – with positive internal building pressure »


Page 117 of 126

Example-Roof Overhang (C & C) »

»


p = (24.46 psf)[(-3.7) – (-0.18)] = -86.10 psf – with negative internal building pressure For the overhang portion of the truss: – Tributary Width = 2’ – Upward force on the entire truss end is: – Zone 2: (-58.21 psf)(2’) = -116.42 plf (upward) – Zone 3: (-94.90 psf)(2’) = -189.90 plf (upward) – These are NOT the loads on the soffit material .

Page 118 of 126

Example-Roof Overhang (C & C) •


Section 30.10 states that the external coefficient for the covering on the underside of the roof overhang (soffit) is the same as the external pressure coefficient on the adjacent wall surface, determined from Figure 30.4-1 or Figure 30.61, as applicable. – Use of the GCp with negative internal pressure yields the greatest upward load on the material on the underside of the overhang on the windward wall. – Use of the GCp with positive internal pressure yields the greatest downward load on the material on the underside of the overhang on the leeward wall. – For this building, assuming effective wind area is the same as for the truss overhang:

Page 119 of 126

Example-Roof Overhang (C & C) »

»


Windward Wall Soffit Material (Figure 30.4-1) – Zone 4 and Zone 5: GCp = +1.0 – p = (24.46 psf)[(1.0) –(-0.18)] = 28.86 psf – acting upward Leeward Wall Soffit Material (Figure 30.4-1) – Zone 4: GCp = -1.1 – p = (24.46 psf)[(-1.1) –(0.18)] = -31.31 psf (acting downward) – Zone 5: GCp = -1.4 – p = (24.46 psf)[(-1.4) –(0.18)] = -38.65 psf (acting downward)

Page 120 of 126

Example- Chemical SILO (MWFRS) • Chemical Silo (Other Structure MWFRS) (Section 29.5) • • •

•

•


Silo Dimensions: h = 20’, D = 5.0’ Welded Steel Tank: smooth sides, no ladder Roof Slope: 1:12 (conical) – Maximum rise: 2.5 inches (consider contribution to wind load, negligible) Unless otherwise listed, parameters for calculation of qz are identical to those for the MWFRS calculations for equipment building. F = qzGCfAf Lbs (Eq 29.5-1)

Page 121 of 126

Example- Chemical SILO (MWFRS)


Page 122 of 126

Example- Chemical SILO (MWFRS) qz = 0.00256KzKztKdV2 (psf) – Kz = 0.90 (Building C&C) (Table 29.3-1) – Kd = 0.95 (Circular Tanks) (Table 26.6-1) – G = 0.85 (Rigid Structure) (Section 26.9) – qz = 0.00256(0.90)(1.00)(0.95)(115)2 = 28.95 psf – Go to Table 29.5-1 » D/√ qz = 5’/Sqrt(28.95psf) = 0.93 < 2.5 » Go to bottom row » h/D = 20’/5’ = 4.0 » Must interpolate between h/D=1.0 and h/D= 7.0 » Cf = 0.75 – F = (28.95 psf)(0.85)(0.75) Af = (18.45 psf)Af – F = (18.45 psf)Af < (16psf)Af –


Page 123 of 126

Example- Chemical SILO (MWFRS) Af = 5’x20’ = 100 ft2 – F = (18.45 psf)(100 ft2) = 1845 Lbs » This is conservative, OR calculate F for increase in pressure as height increases – q15 = 0.00256(0.85)(1.00)(0.95)1152 = 27.34 psf – q(15-20)= 0.00253(0.90)(1.00)(0.95) (115)2 = 28.95 psf » For 0-15’: D/√ qz = 5’/Sqrt(27.34psf) = 0.96 < 2.5 » Cf = 0.75 – F0-15 = (27.34 psf)(0.85)(0.75)Af = 17.43 psf Af > 16 psf Af – F0-15 = (17.43 psf)(5’)(15’) = 1307 Lbs. – F15-20 = (18.45 psf)(5’)(5’) = 461 Lbs. – Total F on Silo: 1307 Lbs + 461 Lbs = 1768 Lbs –


Page 124 of 126

Example- Chemical SILO (MWFRS) Conservative OTM: (1845 Lbs)(10’) = 18,450 ft-lbs – More Detailed OTM: (1307 Lbs)(15’/2)+(461 Lbs)(15’+5’/2) = 17,870 ft-lbs » The taller the structure is, the more important it is to use the stepped wind force approach. –


Page 125 of 126

Questions


Page 126 of 126

ASCE WIND LOAD EXAMPLES.pdf

Recommend Documents