Project 1 - Design of a structural system for a building

Aim:

To manually calculate the total imposed loads, dead loads acting in a tall building based on given parameter. To assume the dimensions of the structural member for the given spans and load magnitudes. Also to calculate the earthquake base shear at the foundation level for the given site criteria.

Data:

Material properties

Concrete density 24 kN/m3

RCC density 25 kN/m3

Concrete cube strength 50 N/mm2

Assumed steel grade Fe500

Floor to floor height 3.5 meter

Functionality

Ground floor (Retail area)

Level 1 to 29 (Office)

Level 30 (MEP)

Level 31 to 50 (Residential)

Level 51 (Roof-MEP)

Facade

From ground to Level 50 with 1 kN/m2 to be calculated from elevation

Other Acting gravity loads referring to given Data and ACI reference

	Finishes	Partition	Live load	Live load reference
Retail	2 KPa	2 KPa	4.79 kPa	ASCE 07-16 (Table 4.3.1)
Office	2 KPa	2.5 KPa	2.4 kPa	ASCE 07-16 (Table 4.3.1)
MEP	2 KPa		6 kPa	ASCE 07-16 (Table 4.3.1)
Residential	2 KPa	4 KPa	1.92 kPa	ASCE 07-16 (Table 4.3.1)

*Note: Common central staircase areas will be considered 4.79 kPa load apart from selfweight.

Seismic Design parameter

Site class-D

Spectral acceleration Ss = 0.4 g

Spectral acceleration S1 = 0.18 g

Long transition period Tl = 8 second

Provided floor plan:

Total floor area: 30x30 = 900 m2

Service area: 10x10 = 100 m2

Occupancy area: 800 m2

Service area imposed loads per floor:

= 100 x 4.79 = 479 kN/m2

Retail area imposed loads per floor:

= 800 x 8.79 = 7032 kN

Office area imposed loads per floor:

= 800 x 6.9 = 5520 kN

MEP area imposed loads per floor:

= 800 x 8 = 6400 kN

Residential area imposed loads per floor:

= 800 x 7.92 = 6336 kN

Average slab thickness according to ACI-318-19

Minimum RC slab thickness for 10 meter span in outer zone (One end continuous) = l/24 = 10000/24 = 416

We assume 425mm slab thick

Slab load per floor = 800 x 0.425 x 25 = 8500 kN

Minimum RC slab thickness for 3.75 meter span in core zone (One end continuous) = l/24 = 3750/24 = 156

We assume 150mm slab thick

Slab load per floor = 100 x 0.15 x 25 = 375 kN

Total slab selfweight per floor = 8500+375 = 8875 kN

Average beam size according to ACI-318-19

Minimum RC beam thickness for 10 meter span in outer zone (both end continuous) = l/21 = 10000/21 = 476

We assume 475mm thick beam and 450mm width

Overall length of beam in perimeter = 120 meter

Total beam selfweight per floor = 120 x 0.45 x 0.475 x 25 = 641 kN

Facade load per floor:

perimeter x height x density = 120 x 3.5 x 1 = 420 kN

Load tributory for the given floor:

Overall imposed + selfweight load from ground floor:

= 7032 + 8875 + 641 + 420 = 16968 kN

Overall imposed + selfweight load from total office floors:

= 29 x (5520 + 8875 + 641 + 420) = 448224 kN

Overall imposed + selfweight load from MEP floors:

= 6400 + 8875 + 641 + 420 + (6400+8875+641) = 32052 kN

Overall imposed + selfweight load from total residential floors:

= 20 x (6336 + 8875 + 641 + 420) = 323440 kN

Total load of building (excuding column & core walls):

= 16968 + 448224 + 32052 + 323440 = 820684 kN

Dividing the floor area to be half distributed to columns and the other half to walls. Then, evenly assuming all column carries equal loads.

= (820684 / 2) / 12 = 34195 kN

Considering factored axial load per column = 34195x1.5 = 51292 kN

Column assumptions and other details:

Concrete grade M50 = 50 N/mm2

Steel grade Fe500 = 500 N/mm2

Minimum steel percentage 0.8% (with initial assumption of size 1000x1000, we get 8000 mm2)

As per clause 22.4.2.2 from ACI-318-19

51292x1000 = 0.85x50 (A+8000) + (500x8000)

A = 1104752 mm2

Average size of column = 1051 mm

Considering other lateral effects also, we can have initial sizing of column with 1200x1200 mm.

Structural system:

Beam-Slab system with inner core lateral resisting system

• Since the slab is having single bay, beam system will be very easy to distribute the forces to all columns and walls. The central wall will be considered for all lateral loads whereas the gravity shall be diverted to columns.
• Beam system will also increase the stiffness of the single bay slabs whuch are otherwise be flexible.

Proposed structural arrangment for the given floor:

Calculation of seismic base shear:

From ASCE 07-16 section 12,

Sds = 0.4 g

R = 5

I = 1.5

Cs = 0.4 x 1.5 / 5 = 0.12

Base shear V = Cs x W

W = seismic weight of building = 1 x (selfweight + dead loads) + 0.25 x live load

Column selfweight = 1.2 x 1.2 x 25 x 51 x 3.5 = 6426 kN

Assuming half of the column loads from live loads,

Average live load per column = 34195/2 = 17097 kN

25% of live load = 0.25 x 17097 = 4274 kN

W = 17097 + 4274 + 6426 = 27797 kN

Base shear per column V = 0.12 x 27797 = 3335 kN

Conclusion:

Thus, all the relevant calculations for the floor load, structural member dimensions & base shear are carried out and provided in the report.