Design considerations on the influence of slab continuity on punching resistance of flat slabs

Oliveira, Fernanda Gabriella Batista Santos; Soares, Luis Fernando Sampaio; Vollum, Robert Lars

doi:10.1590/S1983-41952020000600015

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ORIGINAL ARTICLE • Rev. IBRACON Estrut. Mater. 13 (6) • 2020 • https://doi.org/10.1590/S1983-41952020000600015 copy

Design considerations on the influence of slab continuity on punching resistance of flat slabs

Considerações de dimensionamento sobre a influência da continuidade na resistência à punção de lajes lisas de concreto armado

Authorship SCIMAGO INSTITUTIONS RANKINGS

abstract:

This paper assesses the influence of slab continuity on the punching resistance of a realistically proportioned flat slab floor plate without shear reinforcement. The edge column punching resistance of a symmetric flat slab extending bays in each direction was assessed by means of NLFEA with TNO DIANA, MC2010 levels II, III, IV, Eurocode 2 and NBR 6118. Both Eurocode 2 and NBR 6118 are seen to give similar predictions for punching resistance, while MC2010, which is based on the Critical Shear Crack Theory and depends on how rotations are calculated and FE modelling assumptions, varies significantly with its levels of approximation with Level IV agreeing reasonably well with predictions from NLFEA. Direction for the critical rotations is shown to vary and can also be influenced by the reinforcement over the span. For EC2, NBR 6118 and MC2010 LoA II and III punching shear design are independent of span, unlike the results obtained with MC2010 LoA IV.

Keywords:
punching shear; slab continuity; NBR 6118; Eurocode 2; MC2010

Slabs	Column size (edge and internal) (mm)	h (mm)	d (mm)	$ρ_{c2+3h}^{*}$ %	f_c (MPa)	Failure Load (kN/m²)	Failure Mode and Location	Failure Shear Force (kN)	Remarks
S1	250x250	150	114	1.41	28	15.54	Punching at internal column	399	No Shear Studs
S2	250x250	150	114	1.41	33	19.97	Punching at edge column	164	Studs at edge and internal column

Slabs	V_Rd,c (kN)
Slabs	Longitudinal	Transverse
With Cladding Load	290	257
Without Cladding Load	240	260

	MC2010						EC2		NBR 6118
	k_e = 0.7
	$\frac{Longitudinal}{Transverse}$			$\sum_{1 {.5d}_{v}} A_{sw}$ [mm²]
	LoA IV	LoA III	LoA II	LoA IV	LoA III	LoA II	$V_{Rd,c}$	$\sum_{1 {.5d}_{v}} A_{sw}$ [mm²]	$V_{Rd,c}$	$\sum_{1 {.5d}_{v}} A_{sw}$ [mm²]	$V_{flex}$
ρ_sup = 1.0%	$\frac{-}{-}$	$\frac{274 .44}{144.22}$	$\frac{142.94}{155 .48}$	-	1358.52	1364.83	267.98	1107.72	313.97	1091.32	424.77
ρ_span = 0.3%	$\frac{-}{-}$			-							424.77
ρ_sup = 1.0%	$\frac{285}{260}$			788.18^b							546.37
ρ_span = 0.6%	$\frac{285}{260}$			788.18^b							546.37
ρ_sup = 1.0%	$\frac{310}{262}$			778.33^b							759.68
ρ_span = 1.2%	$\frac{310}{262}$			778.33^b							759.68
ρ_sup = 0.8%	$\frac{-}{-}$	$\frac{246 .43}{144.22}$	$\frac{117.80}{155 .48}$	-	1358.52	1488.67	260.09	1132.20	301.81	1126.4	420.69
ρ_span = 0.3%	$\frac{-}{-}$			-							420.69
ρ_sup = 0.8%	$\frac{290}{257}$			802.96^b							542.29
ρ_span = 0.6%	$\frac{290}{257}$			802.96^b							542.29
^a ρ_sup = 0.8%	$\frac{240}{260}$	$\frac{254 .95}{172.55}$		886.70^b	1218.97						542.29
ρ_span = 0.6%	$\frac{240}{260}$	$\frac{254 .95}{172.55}$		886.70^b	1218.97						542.29
ρ_sup = 0.8%	$\frac{315}{262}$	$\frac{246 .43}{144.22}$		778.33^b	1358.52						755.61
ρ_span = 1.2%	$\frac{315}{262}$	$\frac{246 .43}{144.22}$		778.33^b	1358.52						755.61
ρ_sup = 0.5%	$\frac{-}{-}$	$\frac{192 .74}{144.22}$	$\frac{79.59}{155 .48}$	-	1358.52	1676.90	252.21	1153.62	279.71	1190.19	414.34
ρ_span = 0.3%	$\frac{-}{-}$			-							414.34
ρ_sup = 0.5%	$\frac{275}{255}$			812.81^b							535.95
ρ_span = 0.6%	$\frac{275}{255}$			812.81^b							535.95
ρ_sup = 0.5%	$\frac{309}{262}$			778.33^b							749.25
ρ_span = 1.2%	$\frac{309}{262}$			778.33^b							749.25

IBRACON - Instituto Brasileiro do Concreto Instituto Brasileiro do Concreto (IBRACON), Av. Queiroz Filho, nº 1700 sala 407/408 Torre D, Villa Lobos Office Park, CEP 05319-000, São Paulo, SP - Brasil, Tel. (55 11) 3735-0202, Fax: (55 11) 3733-2190 - São Paulo - SP - Brazil
E-mail: arlene@ibracon.org.br

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[1] Corresponding author: Fernanda Gabriella Batista Santos Oliveira. E-mail: fernandagbso@gmail.com

$f_{ck}$	30 MPa
$γ_{c}$	1.5
$f_{yk}$	500 MPa
$E_{s}$	200 GPa
$γ_{s}$	1.15
$d_{1}$ ^a	212 mm
$d_{2}$ ^b	196 mm
Self-weight	6.25 kN/m²
Superimposed dead load	1.5 kN/m²
Imposed load	2.5 kN/m²
Cladding load	10 kN/m
Edge Column (2A)	250 mm x 400 mm
Internal Column (2B)	400 mm x 400 mm
$k_{e}$	0.7
$k_{dg}$	0.89