Iranian Code Research Articles

Provisions Comparison of The National Building Regulations (The Eighth Topic) and Iranian Code of Practice for Seismic Resistant Design of Buildings (2800 Standard) for Masonry Buildings with Ring Beam

Provisions Comparison of The National Building Regulations (The Eighth Topic) and Iranian Code of Practice for Seismic Resistant Design of Buildings (2800 Standard) for Masonry Buildings with Ring Beam

Cyclic behavior of the reinforced concrete shear walls with opening retrofitted with steel plate

AbstractThe reinforced concrete (RC) shear walls are widely used as the lateral load‐resisting system due to their adequate ductility and great energy dissipation capacity. On the other hand, use of these walls can reduce the size of the beams and columns and also, decreases the lateral displacements. However, presence of the openings in the shear walls alters the behavior of the wall and therefore, the dimensions and position of the opening play a key role in the performance of this structural system. In this study, an RC shear wall with eccentric opening was verified using ABAQUS software. This model, which is called the reference model, a wall and a pier have been created according to aspect ratios given by ACI318‐14. This model was retrofitted with the steel plates arranged in various patterns and effect of each pattern on the system's performance was investigated and the best one was selected. The best steel plate arrangement increased the ultimate strength, maximum strength, cracking strength, and energy dissipation capacity by 127.3%, 13.42%, 22.53%, and 16.8%, respectively. To practically use this retrofit technique, three low, mid, and high‐rise buildings designed based on the old and new versions of the Iranian Code of Practice for Seismic Resistant Design of Buildings (Standard 2800) were upgraded with this technique and their performance was evaluated and performance of the substandard and standard buildings were compared with each other. The research results showed the ST52 steel plates do not considerably increase the maximum and cracking strength and could enhance the ultimate strength insignificantly. By retrofitting the edges of the openings by the diagonal steel plates and preventing spread of the cracks at the edges and corners, satisfactory results could be attained. Simultaneous use of the vertical and horizontal plates is an effective solution to increase the flexural and shear capacity of the structure.

Probabilistic Seismic Performance Assessment of Tall RC Special Moment-resisting Frame Buildings Equipped with Buckling-restrained Braces under Near-field Excitations

Many tall buildings have already been constructed near faults throughout the world, several of which have sustained casualties and economic losses during strong ground motions. This study investigates the effect of near-fault excitations on the vulnerability of tall, reinforced concrete (RC) special moment-resisting frame (SMRF) buildings equipped with buckling-restrained braces (BRBs) using seismic fragility curves. After attaining the structure’s response modification factor (R), three-dimensional (3D) models of 15-, 25- and 35-story frames were developed by the OpenSees software according to the Iranian code provisions. Thus, the seismic response of the elements was obtained. Subsequently, incremental dynamic analysis (IDA) was conducted by selecting a suitable number of compatible accelerograms in two near-field and far-field groups. Considering the maximum story drift as the demand parameter and selecting the interstory drift ratios (IDR) for the slight, moderate, extensive, and complete collapse seismic performance levels proposed by Hazus, IDA curves were plotted. Then, the seismic fragility curves were produced using the structural reliability relations. The median fragility at complete collapse damage level reduced from 0.73g, 0.62g, and 0.61g to 0.68g, 0.59, and 0.57g for the 15-, 25, and 35-story near-field and far-field earthquake models, respectively. This was attributed to increasing vulnerability and seismic fragility of the structures as a result of both height increase and distance reduction from fault. Based on the results, the most vulnerable structure, i.e., the 35-story near-fault model, experienced a 40, 17, 18, and 6% increase in median fragility at slight, moderate, extensive, and complete collapse damage levels, respectively.

The Seismic Performance of Infill and Retrofitted Structural Walls under Earthquakes

To account for the effects of infill walls, the Iranian Code reduces the period of the structure. As a result, filler walls in the plane of structural frames result in significant changes in the properties they possess; therefore, the resistance, stiffness, ductility, distribution of internal forces, and other characteristics of such a frame with an empty frame differ greatly. In this research using 7 far-field earthquakes, a nonlinear time history analysis was performed on reinforced concrete frames with and without masonry infill walls. The maximum relative displacements between the stories were determined. Also, to evaluate the seismic performance of structural masonry walls, the fragility curve of unreinforced masonry walls retrofitted with FRP sheet based on different scenario under the effect of earthquake loads has been investigated by the finite element method. According to the results, the presence of infill walls reduces the number of plastic hinges as well as the maximum relative displacement between the stories. Furthermore, by increasing the number of FRP sheet layers and the reinforced area of the FRP sheet to the entire wall of an unreinforced structural wall, the seismic behaviour of the wall is more effective than other reinforcement patterns and damages the wall less.

Investigating seismic behavior of a modified widened flange beam-column connection in SMRF utilizing experimental, numerical and hybrid simulation

This manuscript presents the seismic performance of a modified widened flange beam-column connection in a special moment-resisting frame (SMRF). The beam-column connection has been modified by two cover plates welded to the top and bottom flanges of the beam and investigated under earthquake acceleration. One-story one-bay special moment resisting frame with an increased beam flange at the vicinity of column was analyzed in accordance with the Iranian Code of Practice for Seismic Resistance Design of Buildings (Standard 2800). Experimental investigation was carried out in which a cyclic displacement history was applied. Numerical finite element analysis was carried out using ABAQUS and its results validated by experimental test results. A hybrid simulation was conducted utilizing OpenSees as the finite element software, OpenFresco as the middleware and LabVIEW as data collector and actuator motion controller. Results comparison of three above mentioned methods (experimental test, numerical analysis and hybrid simulation) indicate that the hysteresis curves are in great compatibility with each other. As expected, results demonstrate that the yielding occurred immediately beyond cover plates at arc shaped areas of beam. On the other hand, the experimental and numerical results show that the specimen reached at least 0.07 rad drift angle before experiencing strength degradation. Furthermore, parametric studies on ‘c’ and ‘R’ which are two key parameters of modified widened flange beam represent that for a constant dimensions of cover plate, increasing ‘c’ and decreasing ‘R’ will reduce plastic strain and stress demands in beam.

Seismic reliability analysis for strengthening of reinforced-concrete hospital building with base isolation Frames

When an earthquake occurs in a region, it causes structural damages to buildings. Retrofitting these damaged structures before earthquakes to happen reduces the potential hazards and minimizes future casualties. In this paper, the seismic assessment of Reinforced Concrete (RC) structures inadequately to withstand seismic loads due to changing demands, and their retrofitting is studied. After a brief introduction of seismic retrofit described for existing structures, methods of assessing the seismic vulnerability of existing buildings are presented. To show the effect of the selected retrofit approach on the seismic behavior of RC buildings, an existing hospital building was selected as the case study. Since the use and occupancy of the selected RC building designed as a residential building had changed, a seismic assessment was carried out using Opensees software to show whether the building needs seismic retrofit or not. After macro modeling to assess the seismic behavior of the structure, the dynamic analysis was conducted by applying 7 earthquake records on soil type B based on Iranian seismic code. Selecting the retrofit approach, which contains using Lead Rubber Bearing (LRB), was performed based on Iranian codes. To consider the uncertainties related to the ground motion, 27 ground motion time histories were utilized and results showed that the building needs seismic retrofit because of the increasing demands. Furthermore, the performed reliability study illustrated an effective role in improving the seismic behavior of the buildings under earthquake loads by the retrofit method.

Evaluation of near-fault effects on the general code spectrum of the Iranian code of practice for seismic-resistant design of buildings, case study: Tehran

Evaluation of near-fault effects on the general code spectrum of the Iranian code of practice for seismic-resistant design of buildings, case study: Tehran

Near‐fault ground motion effects on pounding and unseating using an example of a three‐span, simply supported bridge

AbstractA simple model of a three‐span, simply supported bridge consisting of three rigid decks supported by two axially rigid piers and rigid abutments at two ends is analyzed by solving the dynamic differential equations. The response spectrum method is not considered, and it is assumed that there is no soil–structure interaction. The bridge is acted upon by the acceleration of gravity, g, and excited by differential horizontal‐, vertical‐, and point‐ and cord‐rocking components of near‐fault ground motion. The model's in‐plane linear response shows that the vertical and rocking ground‐motion components have no noticeable effect on the maximum pounding force between bridge segments when computed for horizontal ground motion only. For the model with system periods longer than 1 s subjected to the strong motion pulse corresponding to magnitude M = 7, the vertical ground‐motion component contributes to the destabilizing effect of the gravity. For bridge periods longer than 0.5 s, the simultaneous action of horizontal and vertical ground‐motion components can noticeably increase the minimum gap size required to prevent pounding and the minimum seating length to avoid the unseating of bridge segments when computed for horizontal ground motion only. For system periods shorter than 1 s, the time delay of input ground motion has a significant effect on the minimum gap size to prevent pounding as well as on the minimum seating length to avoid unseating of the deck. The response of the bridge subjected to differential horizontal, vertical, and point‐rocking ground‐motion components is almost the same as the response under differential horizontal and vertical components of the ground motion. The main contribution to changes in the response, which is computed for horizontal ground motion only, is caused by the vertical and cord rocking of the ground motion. The minimum seating length to avoid the unseating of bridge segments suggested in seismic Iranian Code, No: 463 (Road and railway bridges seismic‐resistant design code, 2008), is conservative for pulses with magnitudes M = 5 and 6, but not conservative for bridge periods longer than about 0.6 s and a near‐field pulse with M = 7 magnitude.

Ground-motion simulation for the 2017 Mw7.3 Ezgeleh earthquake in Iran by using the Empirical Green's Function Method

The aim of this study is to investigate the strong ground motion generation of destructive earthquake in Kermanshah with the moment magnitude of 7.3 using Empirical Green’s function (EGF) method. To simulate the ground-motion can be helpful for understanding seismic hazard and reduce fatalities due to lack of real ground motion. We collected the seismograms recorded at seven strong motion stations with good quality to estimate the source parameters at frequencies between 0.1 and 10.0 Hz. By minimizing the root-mean-square (rms) errors to obtain the best source parameters for the earthquake. The earthquake fault was divided into seven sub-faults along the strike and seven sub-faults along the slope. The asperity of 21×10.5 km was obtained. The rupture starting point has been located in the northern part of the strong motion seismic area. The coordinates of the rupture starting point indicate that the rupture propagation on the fault plan was unilateral from north to south. The simulated ground motions have a good correlation with observed records in both frequency and time domain. The results are in well agreement with the Iranian code of practice for seismic resistant design of buildings, however, the calculated design spectrum of Sarpol-e Zahab station is higher than the design spectrum of the Iranian code which suggest that the Iranian code may need to be re-evaluated for this area.

Empirical fragility curves of engineered steel and RC residential buildings after Mw 7.3 2017 Sarpol-e-zahab earthquake

This study investigates the damage data after November 12, 2017, Iran earthquake (Mw 7.3), collected on 440 steel and reinforced concrete residential buildings. Structures have low-to-medium height and are located in Sarpol-e-zahab city, as well as in the west and northwest parts of Kermanshah province, Iran. The peak ground acceleration demands are determined according to data of the micro-shakemap of Sarpol-e-zahab city and the shakemap of Kermanshah province, while the mean values of intensities are determined from the existing empirical relationship between PGA and intensity. The investigated buildings are engineered steel and RC structures nominally erected according to the second and third editions of the Iranian code for earthquake-resistant buildings, but mostly under careless supervision and with low-quality materials. Damage probability matrix, vulnerability index and empirical fragility curves are presented for three subgroups of steel and RC structures on the basis of (i) structural materials and seismic resistant systems (i.e. braced, moment and combination of braced and moment steel frames, as well as moment and combination of moment and shear wall RC frames), without considering the height of structures; (ii) structural materials and height of structures, without considering the seismic resistant systems (i.e. low and medium-height steel and RC structures); (iii) structural materials, without considering the seismic resistant systems and height of structures (i.e. total data for steel and RC frames). The proposed fragility curves are compared with other fragility curves for steel and RC buildings from previous studies. Finally, since this earthquake was the first seismic event in Iran affecting a considerable number of steel and RC engineered buildings, the proposed empirical fragility curves are definitely unique and crucial for realistic damage and vulnerability assessment of similar buildings in future earthquake scenarios, as well as for developing rapid seismic loss assessment after damaging earthquakes.

Seismic behaviour of reinforced concrete frames with steel-plate shear walls

This paper describes an investigation carried out on the behaviour of buildings with a dual lateral load-resisting system, comprising a reinforced concrete (RC) moment frame and steel plate shear walls (SPSW), subject to near-fault (NF) and far-fault (FF) earthquakes. Experimental validation of a one-bay, three-storey, RC frame with SPSWs was done using structural analysis software. The seismic performance of four buildings with various numbers of storeys was then compared using finite-element software. The non-linear dynamic behaviour of the four building was also modelled. Based on the results, it was found that the standard seismic design spectrum defined by Iranian Code of Practice for Seismic Resistant Design of Buildings does not satisfy all structural demands developed by NF earthquakes. The spectrum should be modified, especially for areas near active faults. The results also revealed that the impact of FF earthquakes on low- to mid-rise structures is more profound compared to that of NF earthquakes. Conversely, it was also found that NF earthquakes have greater impacts on taller buildings than that of the FF motions.

Ramifications of blind adoption of load and resistance factors in building codes: reliability-based assessment

This paper presents a probabilistic approach to reveal the negative consequences of overlooking code calibration when adopting the provisions of nonindigenous building codes in design. A taxonomy of the national building codes of various countries whose provisions are adopted from one or more original standards is first presented. Next, the reliability-based approach to quantify the lack of safety that may arise due to the absence of code calibration is presented. This approach is then applied to the case study of the National Building Code of Iran, whose load and resistance factors are directly adopted from ASCE/SEI 7. To this end, seven steel building archetypes with various structural systems at various regions with different seismicity levels and site classes are designed according to the Iranian loading and steel design codes. Subsequently, 2510 structural elements, including beams, columns, and braces, from these archetypes are subjected to reliability analysis to compute their reliabilities. In this analysis, the uncertainty of material properties are quantified using local laboratory test data and the uncertainties associated with manufacturing tolerances of steel elements are quantified through extensive field surveys. The analysis results in reliability indices that are markedly smaller than the targets set by the original standards the Iranian code has adopted from, which exposes the notable lack of safety in the ensuing designs. Subsequently, the load and resistance factors are calibrated to achieve the target reliabilities. Among other changes, the results indicate the need for a 25% increase in the earthquake load factor, which reveals the lack of safety that is implicit in the current practice. Reliability sensitivity analysis is then employed to determine the sources of uncertainty that are most influential on the resulting reliabilities. The presented approach is immediately applicable to the assessment of the building codes of other countries.

Shaking table study on the seismic performance of an Iranian traditional Un-Reinforced Masonry (URM) building

Shaking table experiment for considering the seismic performance of an existing un-reinforced masonry (URM) building with Jack-arch flooring system was performed. This structural system is one of the most common traditional structures, especially in existing traditional school buildings in Iran. The study involved seismic and dynamic identification tests on one model before and after being modified, including URM brick building with two different floor behavior. In the first model, steel tie beams and steel rods were used, according to the recommendation of Iranian Code of Practice for Seismic Resistant Design of Buildings (Standard-2800), to improve the integrity between steel joists and have a stiff diaphragm with continuous loading path. The second model contained a flexible diaphragm. Dynamic identification tests were performed on each model before and after the experiments in order to identify and track changes in their natural period as the experiments progress. Results showed that the integrity of flooring diaphragm had a considerable impact on improving the seismic performance and reducing the seismic vulnerability of URM buildings with respect to control the damage level and limiting the crack occurred in the model. According to the test results, model with integrated stiff in-plane behavior could meet the Life Safety (LS) performance level. The strengthening methodology on the roof distributed the internal forces more appropriately between different elements and took advantage of the strength of different structural elements.

Inertial interaction effects analysis on the estimating of dynamic amplification factor for reinforced concrete structures

This work shows the importance of the need for revision of the Algerian seismic regulations RPA 2003 in terms of the dynamic amplification factor for R/C Rigid buildings with period 0.3 < T < 0.35 in stiff site. In most national building codes, formulas for estimating the seismic base shear include many factors such as the dynamic amplification factor D presented in the Algerian and Moroccan seismic codes RPA2003 and RPS2000 respectively, the response coefficient of the building B for the Iranian code ICS1999, and the spectral acceleration amplification factor B0 for the Eurocode 8. To determine this factor, it is necessary to estimate the value of the vibration period of building based on empirical formulas that do not consider the inertial effects. Diagrams representing the variations of this factor show that the latter remains constant over a range from 0 to 0.7 s for the Algerian code corresponding to structures with 1 to 7 levels; 0 to 1 s for the Moroccan, Iranian and Eurocode 8 corresponding to structures with 1 to 10 levels. No difference was noted in the dynamic factor as a result of degradation of the soil bearing capacity in this ranges. The purpose of this paper revolves around two main themes: the effects of Soil Foundation Structures Interaction (SFSI) on the estimation of dynamic amplification factor on the equivalent static analysis, and the elaboration of a new factor DSAF* called “dynamic site amplification factor” which takes into consideration the SFSI effects, the classifications of the seismic zones and the importance of the structures with application of the Algerian seismic code RPA2003. These values are presented in their simple and easy way to the different users. The results show the importance of these safety coefficients, recommended in the seismic regulations under the effect of SFSI, when the RPA2003 placed in the non-conservative side for the structures belongs to the ranges 0 to 0.7 s.

Progressive Sidesway Collapse Analysis of Steel Moment-Resisting Frames Under Earthquake Excitations

This paper deals with the assessment of seismic collapse capacities and the related collapse durations of steel moment-resisting frames (MRFs). For this purpose, three prototypes of five-story steel structures are studied. These structures are special, intermediate and ordinary moment-resisting frames with high, medium and low ductility, respectively (SMRF, IMRF and OMRF). The structures have been designed in accordance with the Iranian codes. Furthermore, the deterioration effects of strength and stiffness for structural elements have been considered based on the results of reference experimental models. Next, using 22 pairs of far-field ground motion records proposed by FEMA P695 instruction, incremental dynamic analysis is conducted up to the dynamic instability of structures. Afterward, the collapse capacities of these structures are evaluated and compared with the fragility curves. Also, progressive sidesway collapse durations of the structures are estimated under the selected ground motion records. The results show that SMRF has larger collapse capacity than those of the other frames, and can diminish collapse probability by 33.4% and 54.6% compared to IMRF and OMRF, respectively. Moreover, the results reveal that sidesway collapse duration of SMRF is greater than IMRF and OMRF.

Ritualinis mandagumas (ta’ârof) šiuolaikinio Irano visuomenėje ir tarpkultūrinėje komunikacijoje: Teherano šiaurinės dalies atvejis

This paper examines the concept and practices of the Iranian ritual courtesy ta’ârof in northern Tehran, based on field-study findings, and analyses its expression in intercultural communication. It examines how contemporary Iranians perceive ta’ârof, what practices of ritual courtesy are commonly found, and whether configurations of the Iranian code of courtesy remain stable in the changing cultural environment. The study employs the theory of face maintenance and data from Iranian face and diaspora research. It shows emic perceptions of ta’ârof, and reveals its practices in Tehran, alongside tendencies of expression among Iranians living in Lithuania. Key words: ta’ârof, ritual courtesy, capital-city culture, intercultural communication, contemporary Iran.

Reliability of Static and Seismic Design of Near Slope Shallow Foundations Following Iranian Code and Eurocode 7

In geotechnical engineering, probability theory can be implemented regarding a reliability-based design to investigate the probability of failure. In this research, a practical probabilistic approach is used to calculate the reliability of a footing design by applying the first-order reliability method (FORM). The reliability and design risk level of deterministic approaches proposed by Iranian code and Eurocode 7 is evaluated. Both the static and seismic designs have been discussed. The distance of the foundation, both near the crest of the slope and away from it, has also been considered. An entire analysis has been done regarding the three most important different soil types to investigate the effect of soil shear strength parameters on reliability. Although the Iranian code presented a more conservative result than Eurocode 7 did in the static design, there was no tangible difference in the seismic mode. Generally, target reliability was not satisfied in any of the deterministic design approaches. In cases where shallow foundations were located near the crest of the slopes, the difference in the results of RBD and deterministic methods would increase. Finally, it can be concluded that the soil type plays an important role in the results obtained from the Iranian code. In granular soils, the reliability of designs based on Iranian code is low (β = 1.80), so this may be a high risk, which should be considered. On the contrary, the best circumstance (β = 3.40) was related to the foundations that are based on cohesive soils.

Expected seismic fragility of code-conforming RC moment resisting frames under twin seismic events

Seismic design codes require buildings to be designed only for one seismic event, neglecting the possibility of multiple earthquake events. However considerable damage and loss is observed due to aftershocks where buildings have been affected by the first event. The purpose of this research is to introduce fragility curves of code-conforming reinforced concrete moment resisting frames (RCMRFs) under aftershock. Three RC moment resisting frames of 4, 8 and 15 stories, are loaded and designed based on the latest three editions of the Iranian code of seismic design for buildings referred to as Standard No. 2800 (STD-2800). The nine designed frames are then numerically simulated in OpenSees software to perform nonlinear dynamic analysis. Twenty natural ground motion sequences, each including two seismic events, were selected from previous studies for the purpose of nonlinear incremental dynamic analysis. Maximum inter-story drift was employed as a damage index, to capture performance of the RC frames under the sequences. The accepted performance for the collapse level was taken from Iranian instructions for seismic rehabilitation of existing buildings, PBO-Publication No. 360, 2007, which is similar to ASCE 41-13. Seismic fragility values are calculated for the buildings in the second event after being damaged in different first event intensity scenarios. Assuming a log-normal distribution for the failure probability function, corresponding values of mean, μ, and standard deviation, β, for each case are calculated and discussed. Results indicate how the probability of failure in the seismic fragility curves may differ as a result of the effects of a first event scenario. It is also shown how updating the design criteria as well as the height of frames can affect fragility in a second event.

Experimental and numerical modeling of horizontally-bent buried pipelines crossing fault slip

Abstract The behavior and response of pipelines subjected to slip fault movement is studied by numerical simulations as well as experimental setup. A finite element modeling is also developed via ABAQUS software. In this study, an artificial accelerogram is applied to the system and matched against the response spectrum according to the standard No. 2800 (Iranian code of practice for seismic resistant design of buildings, 2014). Three different pipe nominal sizes and thicknesses (1 ½”, 2” and 4”) are considered in the experiments on the shaking table. According to the results, plastic hinge as well as the extremum stress and strain is formed in the fixed soil wedge and at locations close to the fault line. Further, as the pipe D/t ratio increases, the plastic hinge forms further away from the fault line. According to the results, the pipe-soil strain ratio (ep/s) has lower values at larger pipe diameters. Also, the axial strains would be greater for the systems with higher (ep/s) ratios.

Evaluation of Progressive Collapse in Steel Structures Designed Based on Iranian Code of Practice for Seismic Resistant Design Buildings (Standard No. 2800), 4th Edition and Iranian National Building Code 'INBC', Part 10

Evaluation of Progressive Collapse in Steel Structures Designed Based on Iranian Code of Practice for Seismic Resistant Design Buildings (Standard No. 2800), 4th Edition and Iranian National Building Code 'INBC', Part 10