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Practical use of secondary walls such as sidewalls is common because the contributions of secondary walls for stiffness or strength have been recognized. In 2016, “AIJ Standard for Lateral Load-carrying Capacity Calculation of Reinforced Concrete Structures” was published as a draft by Architectural Institute of Japan. In this standard new equations for columns with side walls were proposed. From this viewpoint, the authors have conducted static loading tests of flexurally controlled RC column specimens with single opening in the sidewall, to investigate the effects of openings on strength and deformation capacity of RC columns with a side walls. In this paper, the limitations on location of openings inside sidewalls to avoid their effects on flexural strength and deformation capacity are examined using design equations for flexural strength based on full plastic moment of the column and sidewall. The test results indicate that the proposed limitation line on location of openings to avoid their effects for flexure could be effective for practical design.
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Recently, earthquake damage to non-structural walls has become one of the important issues in Japan. Some buildings were demolished after the 2011 Tohoku Earthquake due to damage of non-structural walls without any significant damage in structural members. After that, several projects were launched to develop a new method to take into account the effect of non-structural walls (hanging, standing, and wing walls). In this paper, experimental test results for beam-column joints with non-structural walls are presented. The objectives of the tests were to investigate the equivalent length and hinge location of beams with hanging and standing walls. The results showed that the yield hinge located at the surface of the wing walls and beam-column joint should be modelled as rigid to estimate the deformation of the beams, regardless of the thickness and height of the wall. A tri-linear modelling method for beams with hanging and standing walls was also proposed, and its applicability was confirmed with the test results.
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The seismic performance of a corner beam-column joint in reinforced concrete frames was studied by testing two three-dimensional corner beam-column subassemblage specimens without slabs under constant column axial load and bi-directional lateral cyclic load reversals. The column-to-beam flexural strength ratio was varied from 1.4 to 2.3 by changing the magnitude of column axial load. Although a sufficient margin to prevent shear failure was provided to a corner beam-column joint in the test, the subassemblage specimens failed in joint hinging after beam and column longitudinal bars and joint hoops yielded. The ultimate joint hinging capacity of a corner joint under bi-directional lateral loading was enhanced by an increase in column compressive axial load, and can be estimated based on the new mechanism proposed by Kusuhara and Shiohara.
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The effects of floor slabs on the flexural strength of beams in reinforced concrete buildings under seismic action were verified through tests of frame assembly specimens. A series of experimental and analytical investigations were conducted from 2010 to 2014 in order to further validate the current design practices in Japan. Loading methods in the past beam component tests were reviewed with probable effects of floor slabs. A special loading set-up was used for the frame assembly specimens consisting of four columns and four beams with lengths of one span and two half spans in two directions. The four columns were loaded laterally and independently at mid-height of the upper storey and supported at mid-height of the lower storey with pin-fixed and pin-roller so that axial elongation of the beams and slab would not be constrained by the lateral forces. It has been found from these new loading tests that the tensile stresses in the floor slab reinforcing bars are generally uniform at the beam critical sections and up to the full slab width for the flexural strength when the slab is subjected to tension bending around one percent storey drift, which is much wider than assumed in the current design evaluation.
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This paper presents an experimental study conducted to investigate the seismic performance and out-of-plane response of three rectangular doubly reinforced ductile wall specimens subjected to an in-plane cyclic quasi-static loading. The specimens were half-scale, representing the first story of four story prototype walls designed according to NZS3101:2006. The experimental program including details of the specimens, material properties, test setup, loading protocol and instrumentation is described. Also, the test observations, with focus on the significant stages of wall response as well as the failure patterns of the specimens, are reported considering the correlation between seismic damage and lateral drift. Two of the specimens failed at 2% drift, and their failure modes comprised of bar fracture, bar buckling, concrete crushing and out-of-plane instability. The failure pattern of the third specimen was pure out-of-plane instability which proved to have the potential to cause sudden collapse of slender ductile walls that are designed to resist other failure modes. In light of the test results, the efficacy of wall design provisions in the New Zealand concrete design standard (NZS3101) associated with the observed failure modes is scrutinised.
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This paper provides an overview and the results of a recent experimental study testing the lateral cyclic displacement capacity of limited ductile reinforced concrete (RC) walls. The experimental program included one monolithic cast in-situ rectangular wall specimen and one monolithic cast in-situ box-shaped building core specimen. The specimens were tested using the MAST system at Swinburne University of Technology. They were tested under cyclic in-plane unidirectional lateral load with a shear-span ratio of 6.5. The specimens were detailed to best match typical RC construction practices in regions of lower seismicity, e.g. Australia, which generally results in a ‘limited ductile’ classification to the Australian earthquake loading code. This reinforcement detailing consisted of constant-spaced horizontal and vertical bars on each face of the wall and lap splices of the vertical reinforcement at the base of the wall in the plastic hinge region. The rectangular wall and building core specimens both achieved a relatively good lateral displacement capacity given the limited ductile reinforcement detailing adopted. The lap splice at the base of the specimens resulted in a somewhat different post-yield curvature distribution being developed. Rather than a typical plastic hinge with distributed cracks being developed, a ‘two crack’ plastic hinge was formed. This consisted of one major crack at the base of the wall and another at the top of the lap splice, with only hairline cracks developing between these two major cracks. The majority of the plastic rotation was concentrated in each of these two major cracks.
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The latest version of the Standard for Structural Calculation of Reinforced Concrete Structures, published by the Architectural Institute of Japan in 2010 [1], allows the design of shear walls with rectangular cross sections in addition to shear walls with boundary columns at the end regions (referred to here as “barbell shape”). In recent earthquakes, several reinforced concrete (RC) shear walls were damaged by flexural failures through concrete compression crushing accompanied with buckling of longitudinal reinforcement in the boundary areas. Damage levels have clearly been shown to be related to drift in structures; this is why drift limits are in place for structural design criteria. A crucial step in designing a structure to accommodate these drift limits is to model the ultimate drift capacity. Thus, in order to reduce damage from this failure mode, the ultimate drift capacity of RC shear walls needs to be estimated accurately. In this paper, a parametric study of the seismic behaviour of RC shear walls was conducted using a fibre-based model to investigate the influence of basic design parameters including concrete strength, volumetric ratio of transverse reinforcement in the confined area, axial load ratio and boundary column dimensions. This study focused on ultimate drift capacity for both shear walls with rectangular sections and shear walls with boundary columns. The fibre-based model was calibrated with experimental results of twenty eight tests on shear walls with confinement in the boundary regions. It was found that ultimate drift capacity is most sensitive to axial load ratio; increase of axial load deteriorated ultimate drift capacity dramatically. Two other secondary factors were: increased concrete strength slightly reduced ultimate drift capacity while increased shear reinforcement ratio and boundary column width improved ultimate drift capacity.
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Recent earthquakes and research have shown that the minimum vertical reinforcement requirements in current concrete standards are insufficient to ensure well distributed cracking occurs in ductile reinforced concrete (RC) walls. To address the deficiencies of existing requirements, new theory was proposed to calculate the minimum distributed and end zone vertical reinforcement required for RC walls to meet current performance expectations. The distributed vertical reinforcement requirement was intended to prevent non-ductile behaviour for walls with low ductility demands, and was derived based on the requirement that nominal flexural strength must exceed the cracking moment capacity. The vertical reinforcement required in the ends of the wall was intended to ensure that well distributed secondary cracks form in the plastic hinge region of walls with high ductility demands, and was derived to ensure that the concrete tensile strength could be overcome by the tensile demands imposed when the vertical reinforcement in the ends of the wall yields. The proposed requirements considered the key parameters that influence the behaviour of walls with minimum vertical reinforcement. In addition, the proposed formulas were compared with current minimum vertical reinforcement limits from different concrete design standards by considering the margin of safety between cracking and nominal flexural strength and the secondary cracking behaviour. The deficiencies of the existing requirements were demonstrated and the proposed requirements were proved to be superior for walls with both low and high ductility demands.
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Most non-structural elements (NSEs) including ceilings, piping, services equipment and cladding systems, etc., are typically prone to failure in the event of relatively low to medium earthquake shakings. The poor performance of NSEs demonstrated in recent earthquake events in New Zealand has revealed a gap in NSE design and construction practices, especially regarding compliance with the NSE performance standard (NZS 4219:2009). This study sought to examine the NZ 4219:2009 and compliance in New Zealand’s construction industry, towards improving the performance of NSEs during earthquakes.Using a face-to-face interview enquiry technique, findings from this study revealed that although majority of the participants consider the NZS 4219:2009 to be very important in improving the performance of NSEs during earthquakes, some shortcomings were also identified: (i) non-compliance with the NZ 4219:2009 by construction professionals; (ii) exclusion of guidelines for specific NSEs from the scope of the NZS 4219:2009; (iii) poor ease of use of the NZS 4219:2009 and other relevant excluded NSE guidelines; and (iv) lack of clarity in the NZS 4219:2009 regarding attribution of ultimate design responsibility for NSE seismic coordination.
As a recommendation, the establishment of a robust, simple-to-use seismic specification document that will provide one-stop specifications for the design and installation of NSEs could be a possible solution to promoting strong compliance practices within the New Zealand construction industry, towards achieving improved performance of NSEs during earthquakes.
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The 1992 advent of the Serviceability Limit State (SLS) was for the purpose of eliminating structural and non-structural damage to buildings subjected to small or moderate Earthquakes (EQs). This goal complimented the prior 1976 goal of minimising life-loss due to large Ultimate Limit State (ULS) EQs.
However, moderate direct damage and large indirect losses occurred to many medium-rise pre-2004’ precast concrete-framed buildings in Christchurch and Wellington CBDs as a result of small or moderate EQ ground motions in 2010 [1-3], 2013 and 2016 [4-6.]
A precedence for a proposed SLS level 1 upgrade was set when Christchurch upgraded to a 50 year recurrence SLS following the 2010-2011 earthquakes [7].
Many modern buildings have been engineered with little regard for SLS [8] nor the goal of eliminating disruption from moderate EQs [9, 10]. The proliferation of SLS building damage and large indirect losses [1] have arisen in NZ primarily because of the specification of a too-small SLS demand which corresponds to a ground motion with 25 year return period and because the Structural Performance factor (Sp) is specified in NZ as 0.7 for SLS, which results in a further 30% reduction of the SLS demand. There are also vulnerabilities in ‘pre-2004’ precast floor-to-beam connection detailing [3].
Cost-benefit analyses show that these building losses may be relieved by first correcting the precast vulnerabilities, then using a SLS limit of 50 year (rather than the current 25 year) return period and/or by specifying Sp = 1. The thus proposed ‘maxi-50 year SLS’ with a drift limit of 0.25%, has the same elastic seismic demand as the 100 year international SLS event [10, 11] (with Sp = 0.7) and will minimise non-structural and business disruption losses in small to moderate earthquakes.
