Why Opening Location Matters: Experimental Insights into Damage Propagation in Masonry Infilled Reinforced Concrete Frames

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Earthquakes continue to expose the vulnerability of reinforced concrete (RC) buildings, particularly those incorporating masonry infill walls with architectural openings such as windows and doors. Although these openings are essential for functionality and occupant comfort, they significantly influence structural stiffness, crack propagation, and overall seismic performance. Engineers have long recognized that masonry infills cannot simply be regarded as non-structural components because they actively participate in resisting lateral loads during seismic events. However, accurately predicting how different opening configurations affect structural damage remains a complex challenge due to the interaction between concrete, reinforcement, masonry, and mortar.

The reviewed study provides valuable experimental evidence on how the size and location of openings influence damage evolution in masonry-infilled RC frames subjected to lateral loading. Rather than focusing solely on ultimate strength, the research establishes damage states based on observed crack development and structural behaviour, offering practical information for seismic assessment, structural design, and post-earthquake damage evaluation. These findings are particularly relevant for structural engineers, researchers, building authorities, and policymakers working to improve the resilience of masonry-infilled buildings in earthquake-prone regions.

Bibliographic Information

Item Information
Article Title Experimental Evaluation of Damage State and Failure Propagation of Infilled Frames under the Opening Effect
Authors Hsu Nandar Htun and Khin Su Su Htwe
Journal Innovation in Engineering
Volume & Issue Volume 1, Issue 2
Publication Year 2024
Pages 96–109
DOI https://doi.org/10.58712/ie.v1i2.11
Publisher Researcher and Lecturer Society
License Creative Commons Attribution 4.0 International (CC BY 4.0)

1. Research Background

  • Masonry infill walls substantially influence seismic behaviour. Although infill walls are often classified as non-structural elements, they interact with reinforced concrete frames during earthquakes and contribute to lateral stiffness, strength, and energy dissipation. Their presence can significantly alter load transfer mechanisms and structural response.
  • Predicting damage in infilled frames remains challenging. The structural response depends on numerous interacting parameters, including frame stiffness, masonry strength, mortar properties, reinforcement details, panel geometry, and the presence of openings. These variables make analytical prediction of damage propagation highly complex.
  • Architectural openings modify structural performance. Windows and doors interrupt the continuity of masonry panels, creating stress concentrations that influence crack initiation, crack propagation, stiffness degradation, and ultimate failure mechanisms. Both the size and location of openings can alter lateral resistance.
  • Existing damage classifications remain limited. Previous studies have proposed several damage-state classifications based on inter-storey drift ratio, crack width, and observed failure modes. However, comparatively fewer investigations have experimentally evaluated damage progression in infilled frames containing different opening configurations.
  • Regional design knowledge remains insufficient. The authors highlight that limited experimental research on masonry infills has been conducted in Myanmar. Consequently, local building codes provide little guidance regarding the seismic behaviour of masonry-infilled reinforced concrete frames with openings, increasing uncertainty in engineering practice.
  • Reliable experimental evidence is essential. Experimental testing remains one of the most effective approaches for understanding crack evolution and structural degradation because it directly captures the interaction between masonry panels, reinforced concrete frames, and lateral loading conditions.
  • The study addresses an important research gap. Instead of evaluating only ultimate strength, this research investigates how different opening locations influence damage evolution throughout loading. It also proposes practical damage-state definitions linked to observable crack characteristics and lateral drift ratios, providing information that may improve structural assessment and seismic performance evaluation.

2. Research Objectives

  • To experimentally investigate the lateral behaviour of masonry-infilled reinforced concrete frames containing window and door openings.
  • To examine how the location of openings (central versus eccentric) influences crack initiation, crack propagation, structural damage, and failure mechanisms.
  • To evaluate the relationship between lateral drift ratio and progressive structural damage under monotonic lateral loading.
  • To establish practical damage-state classifications based on experimentally observed cracking behaviour and masonry deterioration.
  • To compare the structural performance of four different opening configurations using laboratory testing.
  • To provide experimental evidence that can support seismic assessment and future design recommendations for masonry-infilled reinforced concrete buildings.

3. Why This Research Matters

  • Improves earthquake-resistant structural design. Understanding how opening location affects damage progression enables engineers to develop safer reinforced concrete buildings capable of achieving more predictable seismic performance.
  • Supports structural damage assessment. The proposed damage-state definitions provide practical indicators that can assist engineers in evaluating building conditions following earthquake events and determining appropriate repair strategies.
  • Provides evidence for engineering guidelines. Experimental observations contribute valuable data for updating structural design recommendations, particularly in regions where masonry infill behaviour has not yet been comprehensively incorporated into building codes.
  • Enhances infrastructure resilience. Better understanding of crack propagation and failure mechanisms helps reduce structural vulnerability, improve occupant safety, and increase the resilience of buildings exposed to seismic hazards.
  • Supports sustainable construction. Accurate damage prediction allows engineers to distinguish between repairable and irreparable damage, potentially extending building service life while reducing unnecessary demolition and reconstruction.
  • Advances experimental structural engineering. The research demonstrates the value of laboratory-based investigations for validating structural behaviour that is difficult to capture using simplified analytical models alone.
  • Provides practical relevance beyond Myanmar. Although motivated by regional engineering challenges, the findings are applicable to many earthquake-prone countries where reinforced concrete buildings commonly incorporate masonry infill walls with window and door openings.

4. Research Methodology

  • Research Design

    The study employed an experimental structural engineering approach to investigate the seismic behaviour of masonry-infilled reinforced concrete (RC) frames containing window and door openings. Instead of relying solely on analytical or numerical modelling, the researchers performed controlled laboratory testing to directly observe crack initiation, damage progression, structural degradation, and failure mechanisms under monotonic lateral loading. This approach enabled a realistic evaluation of how opening configuration influences structural response.

  • Experimental Specimens

    Four half-scale reinforced concrete frame specimens were fabricated, each representing a different opening configuration within the masonry infill panel. Two specimens incorporated window openings, while the remaining two contained door openings. For each opening type, one specimen featured a centrally located opening and another incorporated an eccentrically positioned opening near the column. This configuration allowed direct comparison of both opening size and opening location under identical loading conditions.

    • Central Window (CW)
    • Eccentric Window (EW)
    • Central Door (CD)
    • Eccentric Door (ED)
  • Materials

    The reinforced concrete frames were constructed using conventional reinforced concrete members combined with hand-made clay brick masonry infills. Half-scale masonry units were produced by cutting full-sized bricks to maintain geometric similarity while preserving representative material behaviour. Mortar was prepared using a cement-to-sand ratio of 1:3, with the water-cement ratio adjusted to obtain appropriate workability during masonry construction.

    Material characterization followed ASTM testing procedures to determine the mechanical properties of concrete, reinforcing steel, masonry units, mortar, and masonry prisms before structural testing. These experimentally determined properties ensured that the structural behaviour observed during testing accurately reflected the characteristics of the constructed specimens.

  • Specimen Geometry

    Each reinforced concrete frame measured approximately 1200 mm between column centre lines and 1350 mm in height above the base beam. The masonry infill consisted of 32 brick layers with mortar joints ranging from 7 to 10 mm in thickness. Window openings measured approximately 457 × 610 mm, while door openings measured approximately 419 × 1067 mm. These dimensions allowed the investigation of different opening percentages while maintaining comparable structural configurations.

  • Material Characterization

    Mechanical properties were experimentally determined before structural testing. The average compressive strength of concrete reached 16.4 MPa, while the longitudinal and transverse reinforcement exhibited yield strengths of 597 MPa and 440 MPa, respectively. Masonry prism compressive strength was measured at approximately 4.17 MPa, accompanied by additional evaluations of brick strength, mortar strength, tensile bond strength, flexural strength, density, water absorption, and elastic modulus. These measurements provided a reliable material database for interpreting structural performance.

  • Loading System

    Monotonic lateral loading was applied using a 500 kN hydraulic jack positioned at the upper corner of the reinforced concrete frame. The loading arrangement simulated the lateral forces experienced during earthquake actions while allowing continuous observation of structural response from initial cracking until crushing failure.

    The base beam was rigidly anchored to the laboratory floor using bolted connections to prevent unwanted movement during testing. A steel bearing plate was installed between the hydraulic jack and the frame to minimize local stress concentrations and ensure uniform force transfer.

  • Instrumentation

    Lateral displacement was continuously monitored using two Linear Variable Differential Transformers (LVDTs) installed at the upper and middle portions of the frame. Throughout the loading process, crack initiation and crack propagation were documented through digital monitoring, allowing detailed observation of structural deterioration and damage evolution at different loading stages.

  • Damage Evaluation

    Rather than evaluating only ultimate structural capacity, the researchers established progressive damage states based on observable crack development. Three principal damage stages were identified experimentally:

    • DS1: Initial small cracking corresponding to the first yield stage.
    • DS2: Development and connection of diagonal cracks representing the elastic-plastic transition.
    • DS3: Cross-shaped cracking accompanied by masonry block crushing, indicating ultimate structural behaviour.

    These experimentally defined damage states were subsequently correlated with lateral drift ratios, enabling practical interpretation of structural performance under increasing lateral deformation.

  • Performance Evaluation

    The structural behaviour of each specimen was assessed through multiple engineering performance indicators, including lateral load capacity, displacement response, lateral drift ratio, crack initiation, crack propagation, crushing behaviour, and failure mechanisms. Capacity curves generated during testing provided the basis for comparing the seismic performance of the four opening configurations.

  • Comparative Analysis

    The experimental results were compared across all four specimens to evaluate the influence of opening size and opening location on structural behaviour. Particular attention was given to identifying differences in stiffness degradation, maximum lateral capacity, crack development, and failure propagation between centrally located and eccentrically positioned openings.

5. Key Findings

Opening Location Influences Structural Capacity More Than Opening Size

One of the most important observations reported in this study is that the location of an opening plays a more significant role in structural performance than its size alone. While both window and door openings reduce the integrity of masonry infill walls, specimens containing eccentrically positioned openings consistently demonstrated higher lateral load capacity than those with centrally located openings.

The experimental evidence suggests that placing an opening closer to the edge of the masonry panel allows a larger continuous compression strut to develop during lateral loading. Consequently, the structural system is able to resist greater lateral forces before severe damage occurs. This finding highlights that opening placement should receive careful consideration during architectural and structural design, particularly in earthquake-prone regions.

Damage Progresses Through Clearly Identifiable Stages

The laboratory observations reveal that structural deterioration follows a consistent sequence of damage development regardless of opening configuration. Initial damage begins with very fine cracks concentrated near stress concentrations around the opening. As loading increases, these cracks gradually extend into diagonal crack networks before ultimately developing into crushing and severe masonry failure.

By linking crack development to lateral drift ratios, the researchers establish practical damage-state definitions that can be applied during structural inspections and post-earthquake assessments. Instead of relying solely on visual judgement, engineers may relate observable crack characteristics to expected structural performance levels.

Eccentric Openings Delay Severe Structural Damage

A clear difference emerged between centrally located and eccentrically positioned openings during progressive loading. Frames containing eccentric openings generally experienced delayed crack propagation and maintained structural integrity over a larger deformation range before reaching ultimate damage.

This behaviour indicates that eccentric opening arrangements distribute stresses more effectively throughout the masonry panel, reducing premature concentration of damage around the opening. Consequently, these configurations exhibit greater lateral resistance and improved deformation capacity compared with centrally positioned openings.

Crack Propagation Reflects Load Transfer Mechanisms

The observed crack patterns provide valuable insight into the internal load-transfer mechanism within masonry-infilled frames. Initial cracking typically originated near opening corners, where stress concentration was highest, before extending diagonally toward the loaded column. As loading increased further, crushing developed within compression zones of the masonry panel, accompanied by progressive degradation of the load-carrying mechanism.

These experimentally observed failure paths confirm that masonry infills actively participate in resisting lateral loads through diagonal compression action rather than functioning merely as architectural partitions. Understanding these crack trajectories can assist engineers in predicting vulnerable regions within existing buildings.

Drift Ratio Provides a Practical Indicator of Structural Performance

The research demonstrates that lateral drift ratio serves as an effective engineering parameter for monitoring structural damage progression. Initial visible cracking generally appeared at relatively small drift levels, while extensive cracking and masonry crushing occurred as drift increased toward ultimate structural response.

Because drift ratio can be measured or estimated during structural evaluations, it provides engineers with a practical quantitative indicator for assessing building performance following seismic events. The experimentally established relationship between drift ratio and observed damage may therefore support more reliable structural condition assessment.

Experimental Evidence Supports More Reliable Seismic Assessment

Beyond comparing opening configurations, the study contributes valuable experimental evidence regarding the interaction between reinforced concrete frames and masonry infill walls under lateral loading. The results demonstrate that structural response depends not only on material strength but also on geometric configuration and opening placement.

These findings strengthen the experimental database available for validating analytical models and may contribute to future improvements in seismic design recommendations, structural assessment procedures, and performance-based engineering approaches for masonry-infilled reinforced concrete buildings.

6. Scientific Contribution

  • Provides experimental evidence on the influence of opening location. While previous studies have extensively examined masonry-infilled reinforced concrete (RC) frames, comparatively few have experimentally investigated how different opening locations influence crack propagation, damage evolution, and structural performance. This study demonstrates that opening location has a greater influence on seismic behaviour than opening size alone.
  • Introduces a practical damage-state classification. The research proposes experimentally derived damage states (DS1–DS3) based on observable crack development, masonry deterioration, and corresponding structural behaviour. These classifications provide engineers with practical indicators for evaluating damage progression during structural assessment.
  • Strengthens the relationship between drift ratio and structural damage. By correlating observed crack development with lateral drift ratios, the study reinforces the use of drift-based performance assessment in evaluating masonry-infilled reinforced concrete buildings subjected to seismic loading.
  • Expands the experimental database for masonry-infilled structures. The laboratory observations contribute additional experimental data describing crack initiation, crack propagation, stiffness degradation, and failure mechanisms under monotonic lateral loading, supporting future analytical and numerical model validation.
  • Improves understanding of load-transfer mechanisms. The observed crack patterns and crushing behaviour provide valuable insight into the interaction between reinforced concrete frames and masonry infills, illustrating how compression struts develop and deteriorate during increasing lateral deformation.
  • Supports performance-based seismic engineering. The findings provide experimentally verified information that may assist engineers in developing more reliable performance-based evaluation procedures for masonry-infilled reinforced concrete buildings.

7. Industrial Implications

  • Supports earthquake-resistant building design. Structural engineers can use the findings to optimize the placement of windows and doors during the design stage, reducing stress concentrations and improving the seismic performance of reinforced concrete buildings.
  • Improves structural assessment after earthquakes. The experimentally established damage states provide practical guidance for engineers conducting post-earthquake inspections, enabling more consistent evaluation of repair requirements and structural safety.
  • Enhances retrofit and rehabilitation planning. Understanding the relationship between opening configuration and damage propagation can assist consultants in selecting appropriate strengthening strategies for existing masonry-infilled buildings.
  • Supports building code development. Regions with limited experimental evidence on masonry infill behaviour may benefit from incorporating these findings into future seismic design recommendations and structural guidelines.
  • Promotes safer architectural planning. Architects and structural engineers should consider opening location during early-stage building design because architectural decisions directly influence structural performance under seismic loading.
  • Contributes to sustainable construction. More reliable prediction of structural damage enables repair rather than unnecessary demolition, helping extend building service life while reducing construction waste and embodied carbon associated with reconstruction.
  • Supports digital structural engineering. The experimentally observed damage characteristics provide valuable benchmark data for validating finite element simulations, digital twins, and structural health monitoring systems used in modern engineering practice.
  • Benefits infrastructure asset management. Facility owners and public agencies responsible for building portfolios may use the reported damage characteristics to prioritize inspections, maintenance, and seismic rehabilitation programmes.

8. Research Limitations

  • The experimental programme was conducted using four half-scale laboratory specimens. Although carefully designed, the structural response of full-scale buildings may be influenced by additional geometric and construction-related factors.
  • The investigation considered monotonic lateral loading rather than cyclic earthquake loading. Consequently, cumulative damage, hysteretic energy dissipation, and stiffness degradation associated with repeated seismic loading were beyond the scope of the study.
  • Only four opening configurations were investigated, focusing on centrally and eccentrically positioned windows and doors. Other opening geometries, dimensions, and multiple-opening arrangements remain opportunities for future investigation.
  • Material properties correspond to locally available construction materials used in Myanmar. Structural behaviour may vary when different masonry units, mortar compositions, reinforcement details, or construction practices are employed.
  • The study concentrated on in-plane lateral behaviour. Out-of-plane failure mechanisms, which may also occur during earthquakes, were not examined within the experimental programme.
  • Environmental effects, construction imperfections, long-term deterioration, and material ageing were outside the scope of the laboratory investigation and therefore were not considered in the reported structural performance.
  • The conclusions are based on experimental observations rather than numerical parametric analyses. Additional computational studies could further explore a broader range of design variables and loading conditions.

9. Future Research Opportunities

  • Investigate the seismic behaviour of masonry-infilled reinforced concrete frames under cyclic loading conditions that more closely simulate actual earthquake actions.
  • Evaluate full-scale structural specimens to verify whether the observed damage mechanisms remain consistent at practical building dimensions.
  • Study additional opening configurations, including multiple windows, combined window-door systems, irregular opening layouts, and larger opening percentages.
  • Develop advanced numerical models capable of accurately reproducing experimentally observed crack propagation and masonry crushing mechanisms.
  • Investigate the influence of different masonry materials, mortar compositions, reinforcement detailing, and construction quality on structural performance.
  • Examine the effectiveness of strengthening techniques, such as fibre-reinforced polymers (FRP), steel retrofitting systems, or textile-reinforced mortar, for improving the seismic behaviour of infilled frames containing architectural openings.
  • Integrate digital image correlation (DIC), computer vision, and structural health monitoring technologies to improve measurement of crack development during laboratory testing.
  • Investigate probabilistic damage models that incorporate experimental observations into performance-based seismic risk assessment.
  • Compare experimentally derived damage-state classifications with existing international seismic design codes and performance-based engineering frameworks.
  • Explore machine learning and artificial intelligence approaches for predicting crack propagation, damage evolution, and structural failure based on experimentally generated datasets.

10. Potential for Public Policy Citation (Overton)

This article demonstrates moderate potential for future citation in public policy documents because it addresses structural safety, seismic resilience, and damage assessment—topics that are directly relevant to government agencies responsible for building regulation and disaster risk reduction. The experimental evidence may support technical reports, seismic design recommendations, infrastructure resilience strategies, and post-earthquake assessment guidelines, particularly in countries where masonry-infilled reinforced concrete buildings are widely used.

The findings may also contribute to national building code revisions by providing experimentally validated information on the influence of window and door openings on structural performance. Such evidence is particularly valuable for developing countries seeking to strengthen seismic design provisions based on locally relevant experimental data.

However, the article is less likely to be directly cited in broader manufacturing policies, industrial roadmaps, or innovation strategies because its primary contribution lies within structural and earthquake engineering rather than industrial production or technology policy. Its strongest policy relevance therefore lies in structural safety regulations, disaster mitigation programmes, infrastructure resilience planning, and performance-based building assessment frameworks.

11. Who Should Read This Paper?

  • Structural Engineers. Professionals involved in the design and assessment of reinforced concrete buildings can gain practical insights into how window and door openings influence structural behaviour during lateral loading.
  • Earthquake Engineering Researchers. Researchers investigating seismic performance, masonry infill behaviour, damage mechanics, and structural resilience will find valuable experimental observations that can support future analytical and numerical studies.
  • Graduate Students. Master's and doctoral students studying structural engineering, civil engineering, earthquake engineering, and construction materials can use this paper as a reference for experimental research methodology and damage evaluation.
  • Building Code Developers. Organizations responsible for developing or updating seismic design provisions may use the reported findings as supporting evidence for improving recommendations related to masonry-infilled reinforced concrete structures.
  • Consulting Engineers. Structural consultants responsible for seismic evaluation, retrofitting, and rehabilitation projects can apply the reported damage characteristics during structural inspections and retrofit planning.
  • Disaster Risk Management Agencies. Government agencies involved in earthquake preparedness and post-earthquake building assessment may benefit from the proposed damage-state classifications when evaluating structural safety.
  • Academics and Educators. University lecturers teaching reinforced concrete design, structural mechanics, masonry engineering, and earthquake engineering may use the study as an instructional example of experimental structural research.
  • Infrastructure Asset Managers. Organizations responsible for maintaining public buildings and critical infrastructure can use the findings to better understand potential damage patterns and prioritize maintenance or strengthening interventions.

12. Final Thoughts

This study provides a valuable experimental contribution to the understanding of seismic behaviour in masonry-infilled reinforced concrete frames containing architectural openings. Rather than concentrating exclusively on ultimate structural capacity, the authors investigate how damage develops progressively throughout the loading process, allowing engineers to better understand the relationship between crack initiation, crack propagation, and structural deterioration. The carefully designed laboratory programme demonstrates that the location of an opening can significantly influence lateral resistance and damage evolution, offering practical knowledge that extends beyond conventional strength-based evaluation.

One of the major strengths of the research lies in its emphasis on observable structural behaviour. By linking experimentally observed crack patterns with lateral drift ratios and proposed damage states, the study provides information that can support structural inspection, post-earthquake assessment, and performance-based seismic evaluation. Although the investigation focuses on a limited number of half-scale specimens under monotonic loading, the findings establish a reliable experimental foundation for future analytical, numerical, and full-scale investigations.

Overall, this paper represents a meaningful contribution to structural and earthquake engineering. It highlights the importance of considering architectural opening configuration during structural design and reinforces the need for closer integration between architectural planning and seismic engineering. Future studies involving cyclic loading, full-scale specimens, and advanced numerical modelling will further expand the practical value of this work, but the present research already offers important evidence that can inform engineering practice, structural assessment, and future seismic design recommendations.

Suggested Citation

UNP–Teknomekanik Style

Htun, H. N., & Htwe, K. S. S. (2024). Experimental evaluation of damage state and failure propagation of infilled frames under the opening effect. Innovation in Engineering, 1(2), 96–109. DOI: https://doi.org/10.58712/ie.v1i2.11

APA (7th Edition)

Htun, H. N., & Htwe, K. S. S. (2024). Experimental evaluation of damage state and failure propagation of infilled frames under the opening effect. Innovation in Engineering, 1(2), 96–109. https://doi.org/10.58712/ie.v1i2.11

IEEE Style

H. N. Htun and K. S. S. Htwe, "Experimental evaluation of damage state and failure propagation of infilled frames under the opening effect," Innovation in Engineering, vol. 1, no. 2, pp. 96–109, 2024, doi: 10.58712/ie.v1i2.11 .

Harvard Style

Htun, H.N. & Htwe, K.S.S., 2024. Experimental evaluation of damage state and failure propagation of infilled frames under the opening effect. Innovation in Engineering, 1(2), pp.96–109. Available at: https://doi.org/10.58712/ie.v1i2.11 .

Vancouver Style

Htun HN, Htwe KSS. Experimental evaluation of damage state and failure propagation of infilled frames under the opening effect. Innovation in Engineering. 2024;1(2):96–109. Available from: https://doi.org/10.58712/ie.v1i2.11

Chicago (Author–Date)

Htun, Hsu Nandar, and Khin Su Su Htwe. 2024. "Experimental Evaluation of Damage State and Failure Propagation of Infilled Frames under the Opening Effect." Innovation in Engineering 1 (2): 96–109. https://doi.org/10.58712/ie.v1i2.11 .

MLA (9th Edition)

Htun, Hsu Nandar, and Khin Su Su Htwe. "Experimental Evaluation of Damage State and Failure Propagation of Infilled Frames under the Opening Effect." Innovation in Engineering, vol. 1, no. 2, 2024, pp. 96–109. https://doi.org/10.58712/ie.v1i2.11 .

Editorial Note

Editorial Note: This blog post is an independent scholarly review intended for educational and scientific communication purposes. It summarizes and discusses the published article in the author's own words while providing full attribution to the original publication, consistent with the principles of the Creative Commons Attribution 4.0 International (CC BY 4.0) license.

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