Proposed structural system for mixed hollow flat slab

Figures & data

Figure 1. Types of traditional R.C. Flooring systems.

Figure 2. Types of hollow-core flooring systems.

Figure 3. Bubble deck slab.

Figure 4. Proposed mixed hollow flat slab systems.

Table 1. Configuration & dimensions for studied cases

Cases	Spans “m”		Col. St. (Drop Width) “m”			Field St. (Ribbed Slab) “m”				Notes
	L1	L2	S1		S2	L1 – S1		L2 – S2
Case 1	7.0	7.0	3.0		3.0	4.0		4.0		No Drop Panel for Edge & Corner Columns
Case 2	9.0	9.0	4.0		4.0	5.0		5.0
Case 3	11.0	11.0	5.0		5.0	6.0		6.0
Cases	Dimensions (cm)				Slab Thickness (cm)
	Span			Col. Sec.	ts; Slab Thick.		td; Drop Thick.		t;Total Thick.		tv; Equiv Thick.
Case 1	700 × 700			40 × 40	25		7		32		18.06
Case 2	900 × 900			50 × 50	29		16		45		20.85
Case 3	1100 × 1100			60 × 60	34		21		55		24.28

Figure 5. Configuration for the studied cases.

Table

Concrete		Steel Reinforcement:
Density = 2.5 t/m^3	Modulus of Elasticity = 210 t/cm^2	Yield Strength = 3600 kg/cm^2
Poisson's Ratio = 0.3	Ultimate Strength = 250 kg/cm^2

Table

Floor Covering = 150 kg/m^2	Average Intensity of Walls = 150 kg/m^2
Live Loads = 300 kg/m^2	Average Density of Foam Blocks = 20 kg/m^3

Figure 6. SAP Results for Real Ribbed Model for Case 2.

Figure 7. Critical punching shear sections.

Table 2. Dynamic characteristics for the two systems

Cases/Modes		Conventional F. S. System	Proposed Mixed System	Reduction Ratio (%)
		Frequency (Hz)	Frequency (Hz)
Case 1	Mode 1	6.73	6.07	9.8 %
	Mode 2	7.23	6.47	10.5 %
	Mode 3	7.28	6.81	6.5 %
Case 2	Mode 1	4.74	4.41	6.9 %
	Mode 2	5.05	4.70	6.9 %
	Mode 3	5.41	5.15	4.7 %
Case 3	Mode 1	3.88	3.48	10.2 %
	Mode 2	4.15	3.71	10.5 %
	Mode 3	4.33	4.09	5.5 %	Impulsive Load Function

Figure 8. Critical Sections for ultimate design moments.

Table 3. Comparisons of ultimate design moments M₁₁ and deflections

Cases		Ultimate Design Moments M11 (m.t)						Max. Deflection (mm)
		Column Strip			Field Strip
		Sec. 1	Sec. 2	Sec. 3	Sec. 1	Sec. 2	Sec. 3	∆act.	∆all.
Case 1	Convent.	+ 7.7	− 40.7	+ 1.8	+ 5.9	− 3.1	+ 0.3	16.7	28.0
	Proposed	+ 5.4	− 35.9	− 0.1	+ 4.2	− 2.2	− 0.5	20.9
	% Ratio	− 29.9	− 11.8	N.A	− 28.8	− 29.0	N.A	+ 25.2
Case 2	Convent.	+ 13.4	− 83.2	+ 1.3	+ 10.5	− 4.9	− 0.1	26.5	36.0
	Proposed	+ 15.6	− 77.5	− 0.6	+ 5.9	− 1.7	+ 0.5	33.9
	% Ratio	+ 16.4	− 6.9	N.A	− 43.8	− 65.3	N.A	+ 27.9
Case 3	Convent.	+ 21.8	− 145.1	+ 1.4	+ 17.1	− 7.8	− 0.7	39.0	44.0
	Proposed	+ 25.0	− 134.0	− 1.8	+ 8.8	− 7.4	− 1.4	49.8
	% Ratio	+ 14.7	− 7.7	N.A	− 48.5	− 5.1	+ 100.0	+ 27.7

Figure 9. Comparison moment results (M₁₁).

Figure 10. Comparison shear results.

Table 4. Comparisons of quantities between proposed system & conventional flat slab

Cases	Concrete Quantity/floor (m^3)		Reinforcement Quantity/ floor (ton)
	Conventional Flat Slab	Proposed Mixed System	Conventional Flat Slab	Proposed Mixed System
Case 1	112.8	95.3	13.2	11.1
Case 2	234.5	200.0	27.0	22.6
Case 3	417.5	357.0	55.2	46.1

Table 5. Reduction ratios between proposed system & conventional flat slab

Cases	Quantity Reduction %/Floor
	Self-Weight	Concrete	Reinforcement
Case 1	14.5 %	15.5 %	15.7 %
Case 2	13.9 %	14.7 %	16.2 %
Case 3	13.9 %	14.5 %	16.4 %

Table 6. Comparisons of ultimate column loads

Cases	Interior Column–Ult. Ld (ton)			Edge Column–Ult. Ld (ton)			Corner Column–Ult. Ld (ton)
	Convent.System	Proposed System	Red. Ratio	Convent. System	Proposed System	Red. Ratio	Convent. System	Proposed System	Red. Ratio
Case 1	110.6	102.9	7.0 %	35.9	33.0	8.1 %	15.5	13.9	10.2 %
Case 2	205.5	190.3	7.4 %	68.6	63.2	7.9 %	26.6	23.9	10.2 %
Case 3	340.6	313.3	8.0 %	113.1	103.8	8.2 %	43.6	39.2	10.1 %

Table 7. Comparisons of dynamic characteristics

Cases	Max. Deflection (mm)			Max. Relative Velocity (mm/s)
	Conventional System	Proposed System	Increase Ratio	Conventional System	Proposed System	Increase Ratio
Case 1	1.9	2.6	36.8 %	4.7	5.9	25.5 %
Case 2	2.7	3.2	18.5 %	5.8	7.2	24.1 %
Case 3	3.7	5.4	45.9 %	7.7	13.8	79.2 %

Table 8. Punching shear results

Cases	Shear Stress (kg/cm^2), sec. 3		Status	tv.sh./ts
	qu.act	quall
Case 1	1.94	7.10	Safe	0.36
Case 2	2.40	7.04	Safe	0.34
Case 3	2.50	7.00	Safe	0.32