Shear performance of high-strength flat slabs with service ducts

Al-khazraji, Mohammed H.; Al-Tameemi, Haider Ali

doi:10.30772/qjes.2026.163723.1679

	Shear performance of high-strength flat slabs with service ducts
Al-Qadisiyah Journal for Engineering Sciences
Volume 19, Issue 3, July 2026, Pages 301-309 PDF (7.33 M)
Document Type: Research Paper
DOI: 10.30772/qjes.2026.163723.1679
Authors
Mohammed H. Al-khazraji; Haider Ali Al-Tameemi^*
Department of Civil Engineering, Faculty of Engineering, University of Kufa, Najaf, Iraq.
Abstract
This study aims to experimentally investigate the two-way shear performance of high-strength concrete flat slabs containing integrated ducts. A total of eight slab specimens containing ducts were manufactured, along with one solid slab functioning as the reference. The experimental program focused on two primary parameters: the horizontal distance of the duct opening from the column face (evaluated at 0, 50, and 100 mm for 50 × 50 mm and 50 × 150 mm openings) and the effect of duct width (evaluated at 50 and 150 mm). The performance of slab specimens was adversely affected by increases in duct width and nearness to the column face. As the duct width expanded from 50 mm to 150 mm, an apparent reduction in load capacity occurred, peaking at 43.9% at the column face. Similarly, closer placement of the duct led to a steeper reduction. Serviceability decreased considerably, with specimens having wider ducts at 0 mm or 50 mm often failing to reach the service load. In contrast, those at 100 mm experienced excessive deflection, up to 94% higher than the control, indicating a severe loss of stiffness. Toughness consistently declined, with a maximum reduction of 51.9% at the column face. It was observed that all slab specimens, even the solid control specimen, exhibited the same failure mode, known as punching failure.
Highlights
The existence of a duct at the column face markedly diminished the slab load capacity. The slab load capacity demonstrated a decreasing pattern with increasing duct width. The presence of ducts significantly affected the serviceability behavior of the slabs.
Keywords
Environmentally sustainable construction; High-strength concrete (HSC); Punching shear; Self-compacting concrete (SCC); Two-way shear slab

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