Access Hatch Cover Slab Design-02!01!2014

STATE OF KUWAIT

SABAH AL SALEM UNIVERSITY CITY

COLLEGE OF EDUCATION FOR WOMEN

PRECAST CONCRETE SLAB FOR ACCESS HATCH COVER

DESIGN CALCULATIONS FOR PRECAST CONCRETE SLABS

Main Contractors:

ARABTEC – COMBINED GROUP JV.

KUWAIT

Drawings Attached:

C0800-SD-0103-01-ST-PR-03-GF-205-001

C0800-SD-0104-01-ST-PR-03-GF-107-001 FOR APPROVAL

C0800-SD-0104-01-ST-PR-04-GF-303-002 NOTE No. : RE – DC - HS

C0800-SD-0104-01-ST-PR-04-GF-104-002 TOTAL 05 + 1 SHEETS. (Excluding pages of Codes & Dwgs.)

Rev. Date. Description.

R1 Dec., 31, 2013 First Submission.

PRECAST CONCRETE SUB-CONTRACTOR:

Real Estate Construction & Fabrication CO., (RECAFCO) P. O. Box 24478, SAFAT,

13105, KUWAIT.

Tel.: 23260054. Fax.: 23260067. e-mail: fm@ recafco.com

SABAH AL SALEM UNIVERSITY CITY

COLLEGE OF ARTS FOR WOMEN / MEN

PRECAST CONCRETE SLABS FOR ACCES HATCH COVER

INDEX

1. General….. Sheet 2

2. Data …….. Sheet 2

3. Precast slab for Access Hatch Cover … Sheet 3

4. Deflection of Access Hatch Cover slab … Sheet 5

Copy of relevant pages from ACI 318 and PCI Design

Handbook Sixth Edition are also enclosed.

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SABAH AL SALEM UNIVERSITY CITY

COLLEGE OF ARTS FOR WOMEN / MEN

PRECAST CONCRETE SLABS FOR ACCES HATCH COVER

General:-

The objective of this design note is to illustrate the design of the

precast concrete slab panel. In general, the precast concrete units

are designed following the principles given in the “PCI Design

Handbook”& ACI 318M-11. Copies of relevant pages are enclosed

herewith for ready reference. The slab panels are designed to support

their self-weight, Finishes and Live loads.

Data:-

Density of concrete = 25 kN/M3

SIDL for Finishes = 3.5 kN/M2 (100mm thick finish only as in DWG)

Live Load = 5 kN/M2

Clear span of slab in Both campuses = 3.50 m.

Max. Effective span of slab = 3.70 m c/c of Supports.

Cube strength of concrete at 28 days = 50 MPa.

Cube strength of concrete at time of stripping = 25 MPa.

As per clause 1.3.1.2, 5.3.3.2 & Eq.5.3.3.1 of PCI Design Handbook,

allowable tensile stress in concrete = 5f’c

For a cube strength of 25 MPa; ft = 5 x 0.82x(25 x 144.86) / 144.86

= 1.88 MPa.

For a cube strength of 50 MPa; ft = 2.66 MPa.

As per ACI 318M-11 clause 10.5.4 & 7.12.2.1 Minimum reinforcement to

be provided = 0.0018 x Cross-section area.

As per Table 5.3.3.1 of PCI Design Handbook, impact factor considered

At time of stripping = 1.3

At time of handling = 1.2

At time of transport = 1.5

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SABAH AL SALEM UNIVERSITY CITY

COLLEGE OF ARTS FOR WOMEN / MEN

PRECAST CONCRETE SLABS FOR ACCES HATCH COVER

Precast slab panel:-

The 250mm thick slab panel is cast on steel mould. It will be

stripped, stacked & transported horizontally. At the site, it will be

erected in position. At all these stages, the slabs will be handled

using the same set of hooks embedded in the slab.

Check for stress conditions at all these stages is carried out in

this design note in the following:

At Stripping Stage:-

(Refer fig. 5.2.5 of PCI Design Handbook – copy attached for ready

reference.)

Using Two point pick-up, IMPACT FACTOR

w = 1.3 x 0.25 x 25 = 8.13 kN/m2.

a = 1.4m; b = 3.86m; b/2 = 1.93m; 15t = 15 x 0.25 = 3.75m.

Mx = 0.0107 x 8.13 x 1.42 x 3.86 / 1.93 = 0.34 kN-m/m.

My = 0.0107 x 8.13 x 1.4 x 3.862 / 0.7 = 2.59 kN-m/m.

Hence, maximum extreme fibre stress = Mmax / Z

= 2.59 x 106 /(1000 x 250

2 /6)

= 0.25 MPa. << 1.88 MPa.

Hence, plain concrete section will be safe. However, as advised by

clause 10.5.4 & 7.12.2.1 of ACI 318M-11, provide minimum

reinforcement of 0.0018 x cross section area.

Area of steel required = 0.0018 x 250 x 1000 = 450 mm2 / m width.

At Transportation Stage:-

The unit will be supported at the same points as at stripping stage.

The only difference in the loading details is the impact factor to be

considered in this case is 1.5 as against 1.3 at stripping stage.

Hence, maximum extreme fibre stress = 1.5 x 0.25 / 1.3 = 0.29 MPa.

This stress is far lesser than the permissible tensile stress of

2.66MPa. Hence it is safe.

At Erection Stage:-

At this stage, the unit will be lifted from the horizontal position

using the lifting hooks at top face of the panel at locations

corresponding to the stripping hooks.

Maximum bending moment and stresses at this stage is same as at the

transportation stage.

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SABAH AL SALEM UNIVERSITY CITY

COLLEGE OF ARTS FOR WOMEN / MEN

PRECAST CONCRETE SLABS FOR ACCES HATCH COVER

Hence, it is safe as plain concrete section. Provided reinforcement

will be adequate.

At Service Stage:-

At this stage, the unit is supported by the RCC frames and the full

effective span is active.

The panel is subject to Live loads in addition to the self weight.

Live load = 5.0 kN/m2.

Self weight of Slab = 1.4x0.25x25 = 8.75 kN/m.

Finishes Loads = 1.4 x 3.5 = 4.90 kN/m.

Live Loads = 1.4 x 5.0 = 7.00 kN/m.

Total service loads = = 20.65 kN/m.

Moment due to total service loads = 20.65 x 3.72 / 8 = 35.34 kN-m.

Therefore maximum extreme fibre stress = 35.34x106/(1400x250

2/6)

= 2.42 MPa. < 2.66 MPa.

However, the panel is designed as RCC slab as per ACI 318M-

11. ( & ACI SP-17M (09) for design Tables)

Ultimate Loads = 1.2 x (8.75+4.90) + 1.6 x 7.00 = 27.58 kN/m.

Mu = 27.58 x 3.72 / 8 = 47.20 kN-m.

B = 1400mm; D = 250mm; d = 250-20-10-8 = 212mm

Provide 7ф16 (=1407mm2) main bars at bottom and ф8 @ 150mm c/c

stirrups.

fc’ = 40 MPa.

Mu / bd2 = 47200000 / (1400 x 212

2) = 0.75 MPa. ρ = 0.20%(Flexure 1)

Ast min. required = 0.33 x 212 x 1400 / 100 = 979.5 mm2.

Ultimate Shear force at critical section =27.58x(3.7/2 – 0.212)

= 45.18 kN.

Bv = 1400 mm; d = 212 mm;

From Clause 11.2.1.1 of ACI 318M-11,

Vc = 0.17 x 1 x (40)1/2 x 1400 x 212 / 1000 = 319.11 kN.

Vc = 0.75 x 319.11 = 239.33 kN. >> Vu

Hence no need for shear reinforcement as per clause 11.4.6 of ACI

318M-11.

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SABAH AL SALEM UNIVERSITY CITY

COLLEGE OF ARTS FOR WOMEN / MEN

PRECAST CONCRETE SLABS FOR ACCES HATCH COVER

Check for Deflection:-

Ref. Clause 8.5.1, 9.5 & sub-clauses thereof of ACI 318M-11.

Ec = 24001.5

x 0.043 x 400.5

= 31975 MPa.

Ig = 1000 x 2503/12 = 13.02x10

8 mm

4. (This is on the conservative side)

fr = 0.62 x 1 x 400.5

= 3.92 MPa.

Mcr = 3.92 x 13.02e8 / 125 = 40.83 kN-M.

Ma = (13.65+7.00) x 3.72 / 8 = 35.34 kN-M.

Ie = 13.02x108 mm

4.

Max. Deflection = 5wL4/384EI = 5 x 20.65x3700

4/(384x31975x13.02e8)

= 1.21 mm.

’ = 7x48.5/(1400x250) = 0.97e-3

2.0 / (1+50x0.97e-3) = 1.908

Total Long-term deflection = 1.908 x 1.21 = 2.31 mm.

L / 240 = 3700 / 240 = 15.42 mm. > 2.31 mm. Hence OK.

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