Seismic Retrofitting of Flat Adobe Vaults in Historic Iranian Windcatchers Using Steel and FRP Bars: A Nonlinear Time-History Analysis Approach for Heritage Conservation

Subject Areas : Seismic Analysis and Design

shima aghakasiri ¹ , Mehdi Shahraki ^{2 *}

1 - Department of Civil Engineering, ST.C , Islamic Azad University, Teharn, Iran.
2 - Department of Civil Engineering, Zah.C., Islamic Azad University, Zahedan, Iran.

Received: 2025-04-21 Accepted : 2025-05-13 Published : 2025-05-21

Keywords: Retrofitting, FRP parts, Flat adobe vault, Heritage conservation, Nonlinear time-history analysis,

Abstract :

The historic windcatcher structures (Āsbaads) of Qal’eh Machi in Sistan, Iran, exemplify the ingenuity of vernacular earthen construction in arid regions. Their flat adobe vaults, central to both structural form and passive cooling function, are increasingly threatened by seismic vulnerability and environmental degradation. Traditional retrofitting methods—such as external bracing or massive overlays—have often proven inadequate, not only due to their intrusive nature but also because they can alter the architectural identity and impose additional loads on the fragile adobe substrate.

To address these limitations, this study investigates the use of Near-Surface Mounted (NSM) Fiber-Reinforced Polymer (FRP) bars as a modern seismic retrofitting solution. FRP systems offer several engineering advantages, including light weight, high tensile strength, and excellent durability against corrosion and moisture, making them highly compatible with adobe structures. The research employs nonlinear dynamic time-history analyses using calibrated finite element models in ABAQUS 2020, applying three real earthquake records (Sarpol-e Zahab, Tabas, and Northridge) representing both near- and far-field ground motions.

Findings demonstrate that FRP retrofitting reduces peak displacement and plastic strain by up to 54% and 48%, respectively, while also achieving up to 52% reduction in base shear. Compared to steel reinforcement, FRP systems consistently deliver better ductility, lower stiffness degradation, and greater energy dissipation under seismic loading. These results confirm that NSM-FRP retrofitting provides a structurally effective and minimally invasive strategy for protecting flat adobe vaults without compromising their architectural authenticity.

This study contributes to the field of heritage conservation engineering by validating a performance-based retrofitting framework that is context-sensitive, technically robust, and culturally appropriate for safeguarding traditional earthen architecture in earthquake-prone regions.

References:

1. Berberian, Manuel. Earthquakes and Coseismic Surface Faulting on the Iranian Plateau. Elsevier, 2014, DOI: 10.1016/B978-0-444-63292-0.09989-0
2. Carozzi, F. G., Milani, G., and Poggi, C. “Mechanical Properties and Numerical Modelling of Textile Reinforced Mortars for Strengthening of Masonry Structures.” Cement and Concrete Composites, vol. 82, 2017, pp. 129–145, DOI: 10.1016/j.cemconcomp.2017.05.016
3. Carozzi, F., Poggi, C., Bertolesi, E., and Milani, G. “Ancient Masonry Arches and Vaults Strengthened with TRM, SRG and FRP Composites: Experimental Evaluation.” Composite Structures, vol. 187, 2018, pp. 466–480, DOI: 10.1016/j.compstruct.2017.12.021
4. Dimitri, R., and Trentinabin, P. “Assessment of Unreinforced Masonry Arch Stability Using Discrete Element Models.” Computers and Structures, vol. 170, 2016, pp. 50–62, DOI: 10.1016/j.compstruc.2016.03.002
5. Faggella, Marco, Paulo B. Lourenço, and Nuno Mendes. “Seismic Performance of Earthen Buildings: A Critical Review.” Construction and Building Materials, vol. 259, 2020, 119725, DOI: 10.1016/j.conbuildmat.2020.119725
6. Lu, Yuchuan, and Dongyang Zhang. “Performance-Based Seismic Evaluation of Heritage Masonry Structures Using Fragility Analysis.” Soil Dynamics and Earthquake Engineering, vol. 141, 2021, 106518, DOI: 10.1016/j.soildyn.2020.106518
7. Toutanji, H. A., and Balaguru, P. N. “Behavior of Large-Scale Adobe Structures Confined with FRP and GFRP.” Journal of Materials in Civil Engineering, vol. 13, no. 5, 2001, pp. 392–399, DOI: 10.1061/(ASCE)0899-1561(2001)13:5(392)
8. Garmeh, M., Ghassemieh, M., and Tehranizadeh, M. “Development of a Self-Centering EBF Using SMA Bolts.” Engineering Structures, vol. 207, 2020, 110250, DOI: 10.1016/j.engstruct.2019.110250
9. Tighiouart, B., Benmokrane, B. and Mukhopadhyaya, P., 1999. “Bond strength of glass FRP rebar splices in beams under static loading”. Construction and Building Materials, 13(7), pp. 383-392, DOI: 10.1016/S0950-0618(99)00037-9
10. Seyedsjadi, S. M. “Natural Environment and Ancient Monuments of Sistan Plain.” Journal of Geographical Research, vol. 56–57, 2019, pp. 146–186.
11. Wang, H., Zha, X., and Ye, J. “Fire Resistance Performance of FRP Rebar Reinforced Concrete Columns.” International Journal of Concrete Structures and Materials, vol. 3, no. 2, 2009, pp. 111–117, DOI: 10.4334/IJCSM.2009.3.2.111