Abstract

Terahertz (THz) and sub-terahertz (sub-THz) waves are unexplored waves between the infrared and microwave ranges. This range features unique characteristics of both light resolution and electromagnetic wave transmission. Sub-THz waves are part of attractive new diagnostic methods for inner objects because they are safer than normal non-destructive inspection methods involving high energy, such as X-rays. In this study, a novel non-contact and non-destructive inspection method for reinforced concrete (RC) structures using sub-THz reflection imaging is proposed to inspect the deterioration of inaccessible damaged RC structures. The results of this study confirmed that the proposed sub-THz imaging method can detect cracks and voids in concrete, as well as in metals inside or behind the concrete, based on differences in reflectance. In addition, the camera-based measurement system makes real-time on-site field measurements possible.

Introduction

In recent years, the deterioration of reinforced concrete (RC) structures has become an issue all over the world. Especially in Japan and other developed countries, large number of social infrastructures built during periods of rapid economic growth are aging significantly ( Alexander and Beushausen, 2019 ). The importance of appropriate maintenance management, including investigation and diagnosis, has been highlighted. In addition, from the perspective of a decarbonized society, it is desirable to avoid demolishing buildings and extend the service life of RC structures through necessary and affordable repairs. Thus, these considerations highlight a growing need for non-contact, non-destructive inspection methods to diagnose infrastructure deterioration without compromising performance. Furthermore, if remote inspection is possible, it is expected to improve measurement efficiency and expand the applicable areas. Therefore, a new inspection method that is not only non-destructive but also non-contact is required.

Several non-destructive and micro-destructive testing methods have been proposed for RC structures. For example, for internal defects that cannot be detected by visual inspection, some of the most widely used methods include percussion inspection ( Kazemi et al., 2019 ), ultrasonic flaw detection ( Lawson et al., 2011 ; Choi et al., 2016 ) and ground penetrating radar (GPR) ( Hugenschmidt and Mastrangelo, 2006 ; Chang et al., 2009 ; Laurens et al., 2005 ; Liu et al., 2020 ; Wiwatrojanagul et al., 2017 ). Table 1 shows a comparison between these methods. During percussion inspection, the concrete surface is knocked, which makes it possible to infer the state of internal deterioration based on the difference in the echo sound. In the case of ultrasonic waves, also a type of elastic wave, it is possible to measure the location of cracks and rebars inside concrete due to differences in acoustic impedance inside the material. Using GPR makes it possible to probe embedded rebars and voids inside concrete owing to its high penetration depth. However, these methods require contact with an object to be measured, which causes measurement problems at elevated or generally inaccessible places, thus highlighting the need for developing a method that can inspect the interior of concrete without contact.

Conclusion

In this study, we conducted measurements using a sub-THz camera to simulate embedded rebar and defects on the surface and inside concrete, assuming that a non-destructive inspection method using sub-THz waves will be applied to reinforced concrete structures. We then conducted actual measurements on real structures. The findings are as follows:

1) An aluminum tape placed on the back of the specimen to simulate the embedded rebar was detected up to 20 mm thickness of the specimen.

2) Field measurements at 10 GHz indicated the possibility of exploring rebars with a cover thickness of approximately 30 mm.

3) In the measurement of specimens with slits simulating cracks, detection was possible for slit widths greater than 1 mm.

4) Even when the slit was hidden by placing a 5-mm-thick mortar, detecting a slit up to 2.5 mm was possible.

5) The reflectance and transmittance varied sensitively with frequency. This fact indicates the potential for more detailed measurement with the selected appropriate frequencies. Further studies are needed to establish their relationship.

6) Camera-based measurement enables areal measurement and real-time monitoring.

7) Downsizing and weight reduction of the measurement system improved its transportability, confirming the possibility of measuring real structures.

Abstract

Concrete’s weak tensile strength renders it susceptible to cracking under prolonged loads, leading to reduced load-bearing capacity and reinforcing bar corrosion. This study investigates the effectiveness of microbial-based self-healing in high-strength concrete, focusing on two bacterial strains: Sporosarcina koreensis and Bacillus. Results demonstrate significant enhancements in micro- and macro-physical properties of high-strength bacterial concrete with Bacillus flexus and S. koreensis, surpassing the control. Bacillus flexus-infused concrete exhibits a remarkable 21.8% increase in compressive strength at 7 days and 11.7% at 56 days. Similarly, S. koreensis-treated concrete shows 12.2% and 7.4% increases at 7 and 56 days, respectively. Enhanced crack healing occurs due to calcite precipitation, confirmed by X-ray diffraction and scanning electron microscopy. Both bacterial strains achieve crack closure within 42 days, with widths of 259.7 µm and 288.7 µm, respectively. Moreover, bacterial concrete from these strains excels in durability against water, acid, and salt exposure, surpassing control concrete. These findings emphasize microbial-based self-healing’s potential in high-strength concrete, providing a practical strategy to enhance structural resilience and extend concrete infrastructure lifespan.

Introduction

High-strength concrete (HSC) has gained widespread recognition for its enhanced mechanical properties, making it suitable for demanding structural applications (Krishnapriya et al., 2015). However, like conventional concrete, HSC is susceptible to cracking under various stress conditions, which can compromise its durability and load-bearing capacity (Iheanyichukwu et al., 2018). The resulting cracks not only diminish load-bearing capacity but also trigger environmental and economic issues, including carbon emissions during repair (Rosewitz et al., 2021). Additional weakness of concrete structure is the presence of voids and fissures in its body matrix. The circumstance of such voids in the matrix of concrete plays substantial role in determining its mechanical properties and durability (Feng et al., 2021; Khaliq & Ehsan, 2016).

The concept of self-healing concrete, facilitated by microbial activity, has emerged as a promising avenue to address these challenges, aiming to autonomously fill and repair such voids and cracks via bio-mineralization. In this process, bacteria induce the conversion of calcium particles within the cement composite into calcium carbonate, calcite. Precipitation and deposition of calcite due to microbial activity of bacteria seals such voids and fissures in the concrete body matrix. This in turn advances the mechanical properties and durability of concrete as well as healing rate of crack formed due variously initiated stress (Rohini & Padmapriya, 2021; Singh & Gupta, 2020). These bacteria must exhibit robust urease activity, withstand high pH levels, and endure mechanical stress within the concrete matrix (Rohini & Padmapriya, 2021; Rosewitz et al., 2021).

Conclusions

This study investigated the impact of microbes on high-strength concrete properties, utilizing B. flexus and S. koreensis. The research encompassed their effect on mechanical strengths (compressive, flexural), ultrasonic pulse velocity, acid and salt resistance, and microbial healing. Key findings are presented as follows:

High-strength bacterial concrete, employing B. flexus and S. koreensis, exhibited improved macro-physical properties compared to conventional concrete. B. flexus concrete showed 21.8% and 11.7% higher compressive strength at 7 and 56 days, while S. koreensis concrete exhibited 12.2% and 7.4% increases. Flexural strength for B. flexus concrete was 6.0% and 9.0% higher at 14 and 28 days, and for S. koreensis concrete, it increased by 5.2% and 6.4%.

Microbial-induced calcite deposition significantly enhanced the healing capacity of cracked bacterial concrete. Within 42 days, B. flexus and S. koreensis concrete restored cracked sections by 259.7 µm and 288.7 µm crack widths, respectively.

Bacterial concrete exhibited greater strength restoration following 55% stress-level crack initiation. While normal concrete regained only 64.0% of its 28-day compressive strength, B. flexus and S. koreensis concrete achieved 96.1% and 94.1% restoration, respectively.

Enhanced durability against acid and salt attacks was observed in bacterial concrete, with reduced weight and strength loss compared to conventional concrete. B. flexus and S. koreensis concrete experienced lower strength losses (4.8% and 5.3% for sulfuric acid, 1.8% and 2.1% for magnesium sulfate) than conventional concrete.

Abstract

This study aims to the practical detection of sub-meter scale voids located inside reinforced concrete structures with different diameters and depths using different frequency antennas of 800, 1000, 1200, and 1600 MHz. The experiment was performed on two concrete blocks with medium-sized voids between 70 and 100 mm diameter, and small-sized voids between 10 and 25 mm diameter. A GPR survey was conducted by dividing each block into two grids of profiles with 50- and 100-mm profile spacing. Then, GPR data was collected along both the horizontal and vertical directions of each block with multi-frequency antennas. The gathered data was processed in 2D and 3D to detect the exact location, dimension, and brightness of these voids. The results showed that GPR has the potential to be quite effective in automating the identification and location of embedded voids within concrete blocks. The accuracy with which the system was able to identify void locations depended mainly on the frequency of the antenna used and the diameter of the void, while the depth of penetration was inversely proportional to the frequency of the used antenna, with estimated depths ranging from 25 cm (using a 1600 MHz antenna) to 1.5 m (using 800 MHz antenna). Moreover, a GPR survey was conducted to evaluate two sites inside residential buildings before and after the rehabilitation process. The radar scan exhibited a notable proficiency in identifying the positions of rebar sites, whether they were situated at a single level or two levels, inside certain areas of construction. The study revealed the ability of GPR to identify the depth of the reinforcing steel within the cement material, particularly in areas where the soil has experienced subsidence.

Introduction

Ground-penetrating radar (GPR) is a well-established characterization and analysis tool in non-destructive test applications ( Brian et al., 2018 ). GPR is now a widely accepted field of scanning technology for surveying and imaging subsurface conditions (Annan, 1992, Tzanis, 2017 , Yang et al., 2020 ). GPR is an effective non-destructive testing method that is characterized by its rapidity, continuity, high detection accuracy, and ability to overcome the shortcomings of the core sampling and impact echo methods. The unique advantage of GPR causes concern for many scholars. Recently, GPR has been used in a wide range of civil engineering and geotechnical applications ( Li et al., 2003 , Rao et al., 2007 , Wu and Chang, 2007 , Rister and Graves, 2008 , Alhasanat et al., 2013 , Tian et al., 2018 ), and in reinforced concrete tests applications, due to its capabilities, benefits and fast performance in the non-destructive exploration of all defects that may be found inside the cement layers.

GPR can also be used to conduct a real-time concrete inspection survey using radar to locate rebar, pipes, tension bars, dowels, and plastic and fiber-optic conduits ( Bungey and Millard, 1993 , Muldoon et al., 2007 , Bala et al., 2015 ). There are few studies on concrete inspection surveys to detect voids/cavities within and under concrete slabs ( Watanabe et al., 2004 , Pollock et al., 2008 , Roger et al., 2011 , Abdul Razak et al., 2015 , Nobes, 2017 ). Radar surveys can be conducted on airport runways, tunnels, abutments, dams, pavements, and garages ( Millard et al., 2002 , Loizos and Plati, 2007 , Evans, 2009 , Lee, 2011 ). Asphalt roads and bridges can also be scanned ( Parry and Davis, 1983 , Maser and Scullion, 1992 , Hugenschmidt and Mastrangelo, 2006 , Loken, 2007 , Hoegh et al., 2015 ). The concrete slabs can be inspected for issues including relative thickness, deterioration, and structural problems ( Roddis et al., 1992 , Loizos and Plati, 2007 )

Results

These two blocks have been surveyed along the same lines to detect the internal voids by different GPR devices such as CX11 (with antenna of 1200 and 1600 MHz), Conquest (with antenna of 1000 MHz), Ramac (with an antenna of 800 MHz), and HandyScan with antenna of 1500 MHz) and the results are then compared.

4.1. Medium-scale void-size (70 mm and 100 mm)

For block No.1, using an 800 MHz antenna, the location of both voids could be detected at a depth of 280 mm for the first void and 200 mm for the second one ( Fig. 3 a). When a 1000 MHz antenna was used the accuracy level of the data increased in the second step for both 2D and 3D, due to the good coverage of the survey concerning the 28-grid lines with a spacing of 50 mm. The first void was represented more accurately in the second step ( Fig. 3 b & 3c) while the level of accuracy decreased significantly concerning 14-grid radar profiles for the same void ( Fig. 3 d & 3e). When a 1200 MHz antenna was used, the depth of penetration increased up to 500 mm ( Fig. 3 f). The degree of brightness decreased in the upper part of block No.1, however, due to the decrease in the frequency range compared to what is considered to be the optimum value in the case of deeper targets. When a 1600 MHz antenna was used, it was noticed that the buried voids could be detected to a depth of 450 mm ( Fig. 3 g). The accuracy level of data decreased with the increasing depth (e.g., see void No.2 which was represented with low accuracy at a depth of 280 mm, and compared with void No.1 at a depth of 200 mm).

Abstract

Durability property is a critical performance indicator of concrete in different environments and locations. However, durability also plays a key role in the sustainability and climate resiliency of concrete structures which is mostly ignored in the context of ways to improve the sustainability of concrete materials and structures. Hence, this paper aims to bring focus to this area by presenting an overview of the critical role of concrete properties especially durability on the sustainability and climate resiliency of concrete structures. This paper first presents a general overview of concrete materials followed by the connection of concrete to sustainability and climate resiliency. Discussions from this paper indicate that to improve concrete sustainability, there is a need to use materials with lower environmental impacts upfront in addition to producing concrete with improved durability to ensure long-term performance. In other words, merely reducing the upfront embodied carbon of materials is not sufficient to achieve sustainable concrete if the impact of such alternative low-carbon materials used to replace the traditional materials in concrete is not considered. On the other hand, the climate resiliency of concrete structures is mostly dependent on improved durability which would sustain their adaptation over time to the impacts of the changing climate conditions. Overall, to achieve sustainability and climate resilience of concrete structures; lower environmental impact, higher durability performance and resilience to applicable climatic conditions must be achieved.

Introduction

Concrete being the most used construction material in the world can be associated with its outstanding performance coupled with its lower cost and availability of raw materials locally in various parts of the world. Concrete has been used extensively to build various infrastructures ranging from transportation systems, health, residential and commercial buildings, water systems, etc. However, the high production and use of concrete have been found to yield negative environmental impacts on the environment due to its contribution to greenhouse gas (GHG) emissions and consumption of natural resources [1] , [2] .

In contrast to other construction materials, such as steel and glass; concrete has a lower unit embodied carbon as depicted in Fig. 1 which shows the carbon emissions per kilogram of each material. However, the production and use of concrete in large quantities have resulted in the concrete industry being a major contributor to the world’s human-induced GHG emissions. A critical part of concrete responsible for the high GHG emission is the production of portland cement (PC) which is the primary binder in concrete and other cementitious materials. Out of all cementitious materials (i.e. concrete, mortar, grout, etc.), concrete consumes PC the most with an estimated amount of 70% while the other 30% is used for other cementitious materials such as mortar, grout, etc.

Conclusion

This paper presents an overview of various properties, specifically the durability of concrete and how it influences concrete sustainability and climate resiliency. Discussions in this paper show that the durability of concrete is very critical to both concrete sustainability and climate resiliency and a holistic approach needs to be employed. Improving the durability of concrete would result in the reduction or elimination of raw material and energy use for rehabilitation and reconstruction resulting in lower environmental impact thereby enhancing sustainability. Similarly, enhanced durability of concrete would ensure that concrete structures can adapt to the changing climate changes thereby improving its climate resiliency.

Thus, to improve the sustainability and climate resiliency of concrete infrastructures; core attention must be placed on the embodied carbon of the materials and the durability performance rather than the former only. Finally, initiatives to improve concrete sustainability and climate resiliency should be specific geographical zone-based rather than a global approach as the availability of raw materials and climate conditions varies with location.

Abstract

     This paper presents a rapid machine learning-based damage detection framework for identifying the damage extent of concrete shear wall buildings. For this purpose, a parametric study was carried out to determine the most efficient machine learning algorithm in classifying the damage states of the building. According to this parametric study, the K-Nearest Neighbor (KNN) learner was selected as the reference prediction model because of the higher accuracy achieved by this algorithm. Bayesian Optimization (BO) algorithm was used to tune the hyperparameters affecting the accuracy of the model. The most efficient attributes were selected from the set of damage indicators through the BO algorithm to train the model. Three different benchmark buildings, including 7-,9-, and 13-story concrete shear wall buildings, were used to evaluate the robustness of the proposed framework. A suite of 111 pair motions, originally developed for the SAC project, were employed to create a generalized dataset. These motions were uniformly scaled from 0.05 g to 1.5 g to expand the intensity range of the events. All the acceleration signals were polluted to 10% noise using white Gaussian signals to simulate the field condition. Results reveal the efficiency of the proposed framework in identifying the extent of damage in concrete shear wall elements of the building. In addition, a parametric study was conducted to illustrate the reliability of two commonly used features, called Cumulative Absolute Velocity (CAV) and the energy ratio between the acceleration response and the input excitation, in determining the damage states of the shear walls under seismic motions.

Introduction

     Assessment of structural safety is essential for post-earthquake restoration. Generally, to evaluate the post-earthquake vitality of the exposed structures, a complete visual inspection is required [1]. Coordination and implementation of the manual visual inspection needs several dedicated teams and monetary resources. In this regard, considerable efforts have been carried out to automate the visual inspection process, e.g., image-based visual inspection [2]. However, such an engineering visual inspection is only able to detect the visible defects that occurred in the structures [3]. This means that some serious invisible damages may be left latent during the visual inspection. The process of identifying and tracking the structural damage is known as the Structural Health Monitoring (SHM) [4,5]. In SHM, damage detection is related to the methods developed for identifying the probable existence, severity, and location of the structural damage. Model-based and data-driven methods are two of the most commonly used strategies proposed for damage detection. Model-based methods generally involve a system identification algorithm paired with a finite element analysis to update the structural model [6]. The performance of the model-based approaches directly depends on the accuracy of the information about the physical properties of the under-study structure. In addition, updating the finite element model based on the physical properties of the structure is computationally expensive for large-scale structures, and rapid condition monitoring could be challenging in this condition [7,8]. On the other hand, data-driven methods apply statistical learning algorithms to the vibration data captured from the structure. This method uses learning algorithms to construct a classification or regression learner for predicting structural damage [9, 10]. Tsou and Shen [11] proposed the use of Neural Networks (NNs) for predicting the severity and location of the structural damage. They used the variations in the modal properties of the structure as the damage feature to identify the damage. Worden et al.

Conclusion

     This paper presented a rapid algorithm for identifying the severity of local damage in the concrete shear wall buildings. A total number of 1884 nonlinear response history analyses were conducted for each building using the SAC motions. A suite of damage indicators was extracted from the acceleration signals to construct the prediction models. A parametric study was carried out to determine the most efficient learner for classifying the damage states of the buildings. The KNN classifier was selected to construct the predictive models because of its maximum accuracy compared to the other algorithms. The Bayesian optimization algorithm implemented to tune the hyperparameters of the classification learners. The main conclusions derived from the study are as below:

Abstract

To promote the development of BIM technology in the field of identification and reinforcement of existing buildings, this paper takes concrete structures as the research object, refers to the current building seismic identification standards, and develops a BIM-based seismic identification system for concrete structures. The research establishes a corresponding data integration platform for the existing concrete frame structure system. Through the secondary development of Revit software, the computer can automatically extract building information and automatically generate a BIM model for seismic identification. The study shows that the program can provide efficient and accurate calculation results in the seismic qualification of concrete frame structures. The seismic test of the concrete structure of the existing building shows that the concrete strength of some components of the building is lower than C20, and the spacing of stirrups in the densified area of some beam components is greater than 100 mm. The seismic structural measures of the building do not meet the requirements. However, the measures and the calculation index follow the relevant regulations. And the calculated values of all programs are highly consistent with the manual calculation results. it can providing a new idea for local earthquake prevention.

Introduction

In China, there are many existing buildings, the new construction area is large every year, and the land area available for real estate development is less and less (Sing, Love, and Liu 2019). As the development of China’s engineering construction moves towards the third stage of maintenance and modernization, the appraisal, reinforcement, and reconstruction of buildings will receive further attention and development (Bong and Rahman 2022). During the long-term use of building structures, due to the natural environment or human factors, material ageing and structural damage will occur, which in turn will affect the durability of the structure and the bearing capacity of components. (Lee, Kim, and Kim 2021). In addition, as people continue to reflect and pay attention to the environment and survival issues, the concept of sustainable development has become more and more popular, and the construction industry must also take a sustainable development path that is in harmony with resources and the natural environment (Santos, Andrade, and Pereira 2019). The construction of new buildings needs to consume a lot of non-renewable resources, and the service life of existing buildings can be extended by employing maintenance and reinforcement, which is in line with the goals of resource protection and the requirements of sustainable development strategies. Repairing and transforming old buildings instead of blindly demolishing them reduces the emission of construction waste and preserves the memory of the city while protecting the ecology

Conclusion

China has many existing buildings, so the research on existing building inspection and appraisal procedures is of great practical significance and has social and economic benefits. Based on ‘Building Seismic Appraisal Standards’ and combined with BIM technology, the research aims to improve the accuracy and efficiency of testing and appraisal, develop the seismic appraisal software for concrete frame structures, and integrate the seismic appraisal software referring to the latest research results of existing building testing and appraisal. The software is adopted in the seismic identification of existing buildings. The research successfully carried out rapid modeling and used the software to check the seismic bearing capacity of the building. During the data collection process, the gap between the design value and the actual value of the frame column reinforcement configuration is between 1mm-9 mm, which meets the relevant error standards, so the data is used in subsequent calculations. Combined with the on-site test data and program identification results, the concrete strength of some components of the building is lower than C20, and the spacing of stirrups in the densified area of some beam components is greater than the minimum value required by the code, so it does not meet the requirements of the ‘Building Seismic Identification Standard’ for the 7-degree zone C in Class building regulations. The seismic bearing capacity of the building can meet the requirements of the relevant codes according to the program calculation results of the control internal force of the components, the ratio of the bearing capacity of each component to the internal force, and the seismic bearing capacity of the building. However, due to the limited time, the software still has many shortcomings. For example, the existing building structures are of various types, and the research is only conducted on the existing concrete frame structure. To realize the automation of the existing building inspection and identification, it is necessary to improve the structure and the type of evaluation object. When conducting seismic analysis, the study did not take into account the reduction in yield strength after corrosion of the reinforcement, and further research and improvement are needed in future studies.

Abstract

     As a key component in composite beams, the studs are prone to fatigue failure under reciprocating load. Fatigue problem is more prominent especially under circumstances of concrete cracking, stud corrosion or with initial damage. Therefore, static and fatigue tests are carried out to study the fatigue properties of push-out specimens with initial defects, including stud damage and concrete cracking. The test results show that the damage of stud has a great influence on fatigue life, while the crack of concrete has a little influence on fatigue life. The damage of stud has a greater influence on fatigue performances compared to static properties. In addition, based on the dissipative energy theory and experimental phenomenon, the roles of stud and concrete in the process of stud fatigue failure and their interaction are summarized. The dissipative energy mainly includes the shear plastic strain energy of the stud, the plastic strain energy of concrete under compression after the stud, and the heat energy generated by the friction between the stud and concrete.

Introduction

     Steel-concrete composite beams have become popular in recent years for use in bridge engineering [1,2]. Under the complicated environment and load, there may be some damage to the composite beam. There might be some damage, such as corrosion, fractures of weld leg and longitudinal or transverse cracks in the concrete deck. The static and fatigue behavior of stud connection is sophisticated and affects the design resistance and stiffness of composite beams [3,4]. The damage of the stud and concrete may have a great influence on the shear fatigue performance of the interface.

      Welding defects significantly lower the shear capacity of studs, as is widely known. There are many types of welding defects that might appear, such as inadequate penetration, absence of fusion, and gas inclusion [5]. To determine how the damage location and degree affected the static behavior and shear capacity of stud shear connections, six specimens with identical geometrical dimensions were investigated by Qi et al [6]. The test findings showed that, in comparison to the shear capacity of normal specimen, a loss of up to 36.6 % and 62.9 % of the shank area might cause a falling shear capacity of 7.9 % and 57.2 %, respectively. The push-out test was simulated using mathematics, and the results of the test were used to validate the study. It was shown that even though the area of the stud had significantly decreased, the shear capacity was not affected by the severity of the damage when the damaged part was placed 0.5d (where d is the shank diameter) from the stud root, based on the numerical model.

Conclusions

     Static and fatigue tests were carried out on studs in steel–concrete composite study the effects of initial damage in stud and concrete on fatigue performance. The following conclusions are drawn:

     1.  Compared with nondestructive specimens, the fatigue life of transverse crack and longitudinal crack specimens were reduced by 22 % and 4.9 %, respectively, which is determined by the stress characteristics of the stud. Transverse crack makes the stud easily in a state of bending and shear composite, while longitudinal crack does not

     2.  Compared with the preset cracks of concrete, the damage of stud and weld collar had more influence on fatigue performance, in which the loss of stud section of 62.9 % leaded to only about 10 % of fatigue life. The initial damage of stud accelerates the damage accumulation in the stable fatigue development stage, while the concrete cracking leads to the increase of residual slip in the early stage.

     3. The existing calculation methods of residual slip are not completely applicable to the test results of different stresses, and most of the calculation results are too small, which requires some modification of their coefficients.

A large number of moment-resisting frame buildings have been or are being constructed. In addition, more are being planned to be constructed all over the world. These types of buildings have various social and functional uses such as parking garages, reception lobbies and any other open air spaces which have no infill masonry walls and called soft or weak storey. Although multi-storey reinforced concrete buildings with open spaces are highly vulnerable to collapse under the effect of lateral earthquake loads, they have become an unavoidable feature for the most of the newly constructed reinforced concrete framed buildings. This may be due to the essential needs of such open spaces particularly in big cities with limitations in land availability. Figure 1 shows a cross section through a frame building with soft storey. These types of buildings are generally designed considering walls as nonstructural elements without regard to the masonry infill wall action. Some of the modern seismic codes and the conventional practices as well neglect the effect of masonry infill wall based on the assumption that it may lead to some conservative results [1]. Some other codes (e.g. IS 1893–2002 [2], IBC2003 [3]) provide a factor to magnify the induced straining actions in terms of bending moments and shear forces. In order to propose a magnification factor for the induced shear at base for a building with soft storey, Scarlet [4] performed an analysis based on two extreme situations in which uniform structures as well as rigid structures with soft storey have been used. Most of structural design practices in Egypt treat masonry infill walls as non-structural elements, and consequently the contribution from stiffness and strength of such elements to the building is neglected during the analysis. Actually, the presence of such infill walls significantly changes the frame action behaviour and results in changing lateral load transfer mechanism. A building with an open storey or sometimes called soft storey is the one that has a stiffness discontinuity due to the significant flexibility of the open storey compared with the adjacent storeys. Several codes defined the stiffness discontinuity in a building storey as the one with lateral stiffness less than 70% of the lateral stiffness of the storey above or less than 80% of the average stiffness of the three storeys above [3,5,6]. Dolsek and Fajfar [7] attempted to explain the reason behind occurrence of soft storey effect in uniformly infilled frames as well as when this phenomenon occurs. Structural models designed according to the Eurocode 2008 together with structures designed with limited strength and ductility according to previous codes have been utilized to perform the analysis. In 2002, Demir and Sivri [8] studied the seismic response of reinforced concrete structures with different configurations of masonry infill in order to show the effects of non-structural masonry infill walls on the induced building’s response.

A major part of earthquake-prone settlement areas in the world comprise sub-standard building stock. These sub-standard buildings, which are typically constructed with poor reinforcement details and low strength concrete, generally suffer from destructive earthquakes, due to their low deformation capacity as well as insufficient lateral stiffness and strength. Moreover, these buildings incorporate various typical deficiencies such as corrosion of reinforcing bars, lack of concrete cover, inadequate reinforcement anchorage conditions and lack of maintenance. In addition to the fact that they generally do not meet the requirements prescribed in modern seismic codes, they also do not fulfill the design requirements at their time of construction. Consequently, in order to prevent potential loss of life and economic losses, and maintain a sustainable development of the built environment, seismic safety attributes of these buildings need to be urgently evaluated using proper methods to categorize whether or not they possess risk of life safety or collapse during severe earthquakes. Reliability of available seismic safety assessment methodologies depends on the modeling and analysis approach followed, and the criteria used in defining acceptable damage levels. In earthquake performance assessment, the algorithms used for structural analysis and the assumed damage limits depend mainly on post-earthquake observations and results of laboratory tests. However, among various other uncertainties, post-earthquake investigations do not provide sufficient information on the earthquake demand parameters on the building, such as internal force and deformation demands on the structural members, unless the building is densely instrumented for structural health monitoring purposes. In the case of laboratory tests, the physical and financial constraints deter the researchers from performing full-scale tests that can more realistically mimic the seismic behavior of actual structures. With field testing of real structures; boundary conditions, uncertainties and randomness in material characteristics and construction practice are more realistically considered. In this context, field tests carried out on real-life structures may emerge as a reasonable alternative for creation of benchmark data for verifi- cation of the available structural analysis approaches and assessment methodologies. Perhaps, the field testing of real structures also has its own challenges such as; less control for the variables, difficulties in supplying adequate excitation force capacity, establishment of strong reaction walls, need for large number of sensors and data collection systems, high dependence on weather conditions, need for a devoted team, and the cost for establishment and running of the test site.