Fatigue Performance of One-Way RC Slabs Strengthened in Flexure with NSM Steel and FRP Bars

Yasser Rifat Tawfic; Yehia Abdelazim Hassanean; Moamen Adel El Hamdy; Ahmed Attia Mahmoud Drar

doi:10.2478/cee-2026-0056

Fatigue Performance of One-Way RC Slabs Strengthened in Flexure with NSM Steel and FRP Bars

Civil and Environmental Engineering

Volume 22 (2026): Issue 2 (June 2026)

By: Yasser Rifat Tawfic, Yehia Abdelazim Hassanean, Moamen Adel El Hamdy and Ahmed Attia Mahmoud Drar

Open Access

|Jun 2026

Figures & Tables

Details of reinforcement of tested slabs before and after strengthening

Table 1:

Data of tested slabs

Slab ID	Type of loading	Repeated loading (kN) *	(fc) MPa	*(f′c) MPa*	(NSM) Strengthening system description
CSS	Static	-------	35	30	Control slab
FCS		-------	34	29	2 (Carbon FRP) bars, ϕ 10mm
FGS		-------	37	32	2 (Glass FRP) bars, ϕ 10mm
FBS		-------	34	29	2 (Basalt FRP) bars, ϕ 10mm
SS		-------	38	33	2 Steel reinforcing bars, ϕ 10mm
CSR	Repeated	30	35	30	Control slab
FCR		60	34	29	2 (Carbon FRP) bars, ϕ 10mm
FGR		52.8	37	32	2 (Glass FRP) bars, ϕ 10mm
FBR		44.75	34	29	2 (Basalt FRP) bars, ϕ 10mm
SR		51.25	38	33	2 Steel reinforcing bars, ϕ 10mm

* The fatigue load was set at 50% of the maximum load of the corresponding static-tested slab.

Table 2:

Mix the amount of concrete

Compressive strength target [MPa]	Compressive strength as measured [MPa]	The ratio of water to cement	Cement [kg/m³]	Sand [kg/m³]	Gravel [kg/m³]	Water [kg or litres]
35	35.6	0.43	450	567.74	1135.47	193.5

Table 3:

Characteristics of mix design

Property	Experimentally	ACI 318 M (2019)
Strength in compression (ƒ’c) [MPa]	30.6	---
Tensile splitting strength (f ‘ct) [MPa]	2.93	2.76 (0.5√f′c)
Rupture modulus (f r) [MPa]	5.93	3.43 (0.62√f′c)
Elasticity modulus (Ec) [GPa]	26	(4700√ f′c)

Table 4:

Results of steel and FRP bars’ tensile tests

Property	Steel	CFRP	GFRP	BFRP
Yield strength [MPa]	560	-----	-----	-----
Ultimate strength [MPa]	700	1600	1200	1100
Elasticity modulus [GPa]	200	130	47.5	41

Table 5:

Epoxy resin’s mechanical characteristics

Properties at 7days and 25°C
Strength of tensile [MPa]	≥ 30
Elasticity modulus [MPa]	10000
Strength in compression [MPa]	≥ 80
Strength of bond [MPa]	≥ 4
Ratio of mixing	3.34A:1B

Preparation of strengthened slabs with different NSM bars

Sketch of sequence of loading versus deformation [1]

Cracks pattern of slabs tested under static loading

Cracks pattern of slabs tested under repeated loading.

Table 6:

Summary of the static and repeated tests in terms of loads and deflection

Slab ID	Cracking load Pcr (KN)	Service load Pser (KN)	Yielding load Py (KN)	Ultimate load Pmax (KN)	R %	Δref	Δref %	Failure type
CSS	31	36	26.7	60	-------	45.44	------	Flexure
FCS	33	48	81.13	120	100	9.9	78.21	Flexure-shear
FGS	33	50	74	105.6	76	9.7	78.75	Flexure-shear
FBS	34	45	41.7	89.5	49.33	11.6	74.47	Flexure-shear
SS	35	58	77.7	102.5	70.83	7.5	83.5	Flexure-shear
CSR	32	31.2	25.8	61.53	2.5	43	5.4	Flexure
FCR	33	55	78.2	133.51	122.52	12.9	71.61	Flexure-shear
FGR	30	42	52.6	89.44	49.1	23.7	47.84	Flexure-shear
FBR	30	54	31.9	96.81	61.35	12.55	72.38	Flexure-shear
SR	31	50	28.3	73.06	21.77	20.8	54.23	Flexure

[i] R: Percentage of increase in the maximum load of tested slab.

[ii] Δ_ref: Deflection of tested slab at maximum deflection value of reference slab.

[iii] Δ_ref %: Percentage of decrease of deflection of tested slab at maximum deflection value of reference slab.

Table 7:

Ductility index of the tested slabs

Slab ID	Δ _y (mm)	Δ _u (mm)	Δ_I	Δ_Inor
CSS	4.3	45.44	10.56	1
FCS	14.75	33.8	2.29	0.22
FGS	14.2	43.5	2.92	0.28
FBS	6.2	36.65	5.91	0.56
SS	10.6	51.45	4.85	0.46
CSR	4.5	51.25	8.78	0.83
FCR	15.15	36.55	2.41	0.23
FGR	21.85	43.55	2.00	0.19
FBR	7.4	48	6.6	0.625
SR	8.9	50.9	5.72	0.54

[i] Δ_y = deflection at yielding load; Δ_u.= deflection at ultimate load; ΔI.= ductility index; ΔI_nor = normalized ductility index.

Comparison between Load mid-span deflection for slabs tested statically

Load mid-span deflection for slabs tested under repeated load and those tested statically

Load mid-span deflection for slabs tested under repeated load and those tested statically (cont.)

The ratio of repeated load to mid-span deflection after a number N of zero, one-half and one million cycles (Pr/∆0.5P, Pr/∆1, Pr/∆2)

Load versus strain induced in NSM bars in slabs tested under static and cyclic loading

Table 7:

Values of energy absorption, and deformability index for tested RC slabs

Slab ID	Δ cr [mm]	Δ f [mm]	Energy absorption	Deformability index
CSS	5.8	45.44	3153	6.83
FCS	3.65	33.8	2968	8.26
FGS	2.85	43.5	2060	14.41
FBS	3.2	36.65	2383	10.45
SS	4.5	26	4150	4.78
CSR	5.5	51.25	3117	8.32
FCR	2.9	36.55	3550	11.6
FGR	4.4	43.55	2475	8.9
FBR	2.85	48	1900	15.84
SR	3.6	54	3420	14

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Articles in this issue

DOI: https://doi.org/10.2478/cee-2026-0056 | Journal eISSN: 2199-6512 (formerly 1336-5835) | Journal ISSN: 1336-5835

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Language: English

Page range: 851 - 868

Submitted on: Oct 2, 2025

Accepted on: Oct 17, 2025

Published on: Jun 19, 2026

Published by: University of Žilina

In partnership with: Paradigm Publishing Services

Publication frequency: 4 issues per year

Keywords:

Fatigue behaviour,

Flexural strengthening,

One-way RC slabs,

NSM technique,

FRP bars

Related subjects:

Business and economics,

Business management,

Industries,

Environmental management

© 2026 Yasser Rifat Tawfic, Yehia Abdelazim Hassanean, Moamen Adel El Hamdy, Ahmed Attia Mahmoud Drar, published by University of Žilina
This work is licensed under the Creative Commons Attribution 4.0 License.

Volume 22 (2026): Issue 2 (June 2026)

Fatigue Performance of One-Way RC Slabs Strengthened in Flexure with NSM Steel and FRP Bars

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