Precast Concrete Diaphragms Research Articles

Pseudo-Dynamic Tests on Frame–Shear Wall Structure with Precast Concrete Diaphragm

In order to study how to improve the spatial action of precast monolithic composite floor slabs, and examine replacing the cast-in-place surface layer for reducing the weight of structure, we used pseudo-dynamic tests on one-quarter scale models of two-span and three-story frame structures. The lateral load tests compared the stresses and displacements with a cast-in-place floor frame–shear wall structure (SJ1) and a precast monolithic floor frame–shear wall structure with X horizontal braces at the bottom of the floor (SJ2). The results show the X horizontal braces can improve the spatial action. Structural integrity (SJ2) as well as the effective transmission of the horizontal force can be ensured by additional X bracing at the bottom of the rigidity of the floor without a cast-in-place concrete topping. The results show that X horizontal braces more effectively transfer horizontal stress, which provides a beneficial reference for similar research.

Investigation on in-plane mechanical behavior of joint connections for discrete connected new-type precast concrete diaphragms

This paper proposes three new types of connectors adopted in discrete connected new-type precast concrete diaphragms (DCNPD). An experimental investigation of innovated connectors under shear load was conducted to evaluate the failure mode, strain and bearing capacity of joint connections in DCNPD. Based on the experimental results, the hairpin connector (HPC) was selected for simulation verification and further analysis under combined loads to provide crucial information on bearing capacity, ductility, reduction rule, deformation and stiffness in order to reveal its working mechanism. The results indicate that three types of connectors can provide effective connection for slab joints. The ideal fracture failure mode of anchor bar or cover plate is realised in all joint connections. The shear capacity of HPC is weakened by simultaneous tension when it is under combined loads. With the increase of tension-to-shear force ratio, the ductility of HPC is improved, and the shear ductility is relatively better. The evaluation of yield displacement and bearing capacity, degradation law in strength, deformation and stiffness of HPC provides a theoretical basis for the development of joint connection and seismic design of DCNPD, which is vital for the application of DCNPD in precast concrete structures.

Highlighting the need for multiple loading protocols in bi-directional testing

Major earthquakes, such as the Canterbury and Kaikoura events recorded in New Zealand in 2010-2011 and 2016 respectively, highlighted that floor systems can be heavily damaged. Quasi-static cyclic experimental tests of structural sub-assemblies can help to establish the seismic performance of structural systems. However, the experimental performance obtained with such tests is likely to be dependent on the loading protocol adopted. This paper provides an overview of the loading protocols which have been assumed in previous experimental activities, with emphasis on those adopted for testing floor systems. The paper also describes the procedure used to define the loading protocol applied in the testing of a large precast concrete floor diaphragm as part of the ReCast floor project jointly conducted by the University of Canterbury, the University of Auckland and BRANZ. Subsequently the limitations of current loading protocols for bi-directional testing are discussed. The relevance of local seismicity on bidirectional demand is demonstrated by examining a large dataset of records from the RESORCE database. It is concluded that bi-directional experimental testing be undertaken using at least two loading protocols that impose different ratios of demand in orthogonal directions.

Seismic design force level for precast concrete diaphragms

This paper provides guidance for determining seismic design force level for topped precast concrete diaphragms. This has been a controversial topic ever since ASCE/SEI 7-16, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, introduced a section titled “Alternative Design Provisions for Diaphragms” and mandated its use for precast concrete diaphragms in buildings assigned to seismic design category C, D, E, or F.

Verification of diaphragm seismic design factors for precast concrete office buildings

A new seismic design methodology has been developed for precast concrete diaphragms. Seismic design factors were used to be applied on top of diaphragm seismic design forces in the current code. These factors, established through extensive parametric studies, align diaphragm design strengths with different seismic performance targets. A simplified evaluation structure with a single-bay plan was used in the parametric studies. This simplified evaluation structure is reasonable and cost-effective as it can comprehensively cover structural geometries and design parameters. However, further verification and investigation are required to apply these design factors to prototype structures with realistic layouts. This paper presents diaphragm design of several precast concrete office buildings using the new design methodology. The applicability of the design factor to the office building was evaluated and verified through nonlinear time history analyses. The seismic behavior and performance of the diaphragm were investigated for the precast concrete office buildings. It was found that the design factor established for the new design methodology is applicable to the realistic precast concrete office buildings.

Effects of diaphragm flexibility on the seismic design acceleration of precast concrete diaphragms

A new seismic design methodology for precast concrete diaphragms has been developed and incorporated into the current American seismic design code. This design methodology recognizes that diaphragm inertial forces during earthquakes are highly influenced by higher dynamic vibration modes and incorporates the higher mode effect into the diaphragm seismic design acceleration determination using a first mode reduced method, which applies the response modification coefficient only to the first mode response but keeps the higher mode response unreduced. However the first mode reduced method does not consider effects of diaphragm flexibility, which plays an important role on the diaphragm seismic response especially for the precast concrete diaphragm. Therefore this paper investigated the effect of diaphragm flexibility on the diaphragm seismic design acceleration for precast concrete shear wall structures through parametric studies. Several design parameters were considered including number of stories, diaphragm geometries and stiffness. It was found that the diaphragm flexibility can change the structural dynamic properties and amplify the diaphragm acceleration during earthquakes. Design equations for mode contribution factors considering the diaphragm flexibility were first established through modal analyses to modify the first mode reduced method in the current code. The modified first mode reduced method has then been verified through nonlinear time history analyses.

Shear behavior and shear capacity prediction of precast concrete-encased steel beams

A novel precast concrete-encased steel composite beam, which can be abbreviated as PCES beam, is introduced in this paper. In order to investigate the shear behavior of this PCES beam, a test of eight full-scale PCES beam specimens was carried out, in which the specimens were subjected to positive bending moment or negative bending moment, respectively. The factors which affected the shear behavior, such as the shear span-to-depth aspect ratio and the existence of concrete flange, were taken into account. During the test, the load-deflection curves of the test specimens were recorded, while the crack propagation patterns together with the failure patterns were observed as well. From the test results, it could be concluded that the tested PCES beams could all exhibit ductile shear behavior, and the innovative shear connectors between the precast concrete and cast-in-place concrete, namely the precast concrete transverse diaphragms, were verified to be effective. Then, based on the shear deformation compatibility, a theoretical model for predicting the shear capacity of the proposed PCES beams was put forward and verified to be valid with the good agreement of the shear capacities calculated using the proposed method and those from the experiments. Finally, in order to facilitate the preliminary design in practical applications, a simplified calculation method for predicting the shear capacity of the proposed PCES beams was also put forward and validated using available test results.

Precast Diaphragm Response in Half-Scale Shake Table Test

This paper summarizes key diaphragm response parameters observed during the shake table testing of a three-story precast concrete structure built at half-scale. The test structure geometry possessed an aspect ratio in plan and structural wall layout to form a diaphragm-critical condition. Each floor of the structure incorporated a different precast concrete diaphragm construction technique: untopped double tees, topped hollowcore, and topped double tees. A new seismic design methodology was used to design and detail the diaphragms. The test structure was subjected to input ground motions of increased intensity in a series. The series totaled 16 strong ground motions, consisting of design basis and maximum considered earthquakes for which the diaphragms were designed. The primary objectives of the testing program were to examine the behavior of precast diaphragms within the structural system, demonstrate the seismic performance of the precast diaphragms designed with the new design methodology, and calibrate analytical models for the wider research program. This paper describes diaphragm global and local responses. The responses were interpreted in terms of expected diaphragm performance. Design conclusions were drawn based on the observed diaphragm seismic response.

A preliminary study of seismic risk assessment shortly after the Banjarnegara Indonesia earthquake on 2018

This paper presents a preliminary study of seismic risk assessment in Kertosari village, Kalibening Subdistrict, Banjarnegara District, after the earthquake incident on 18th April 2018. The study was based on Hazard US (HAZUS) with Damage Probability Matrix to estimate losses of damage state with model building type (Reinforced Concrete Moment Resisting Frames-Low Height (C1L), Reinforced Masonry Bearing Walls with Wood or Metal Deck Diaphragms-Low Height (RM1L) and Reinforced Masonry Bearing Walls with Precast Concrete Diaphragms (RM2L)). From the results, the probability calculation of damage in Kertosari Villages, moderate damaged category is the most. Other damage categories are slight, extensive, complete and none. Meanwhile, based on site preliminary survey and data from Banjarnegara Municipal Disaster Management Authority [1] which has updated on 20th April 2018 in Kertosari village, complete damaged category is the most. Therefore, it is necessary an expert’s judgment to refine building type model and the criteria of damage state for compatible Indonesian building.

Establishment of performance‐based seismic design factors for precast concrete floor diaphragms

SummaryThis paper presents an analytical study used to establish design factors for a new seismic design methodology for precast concrete floor diaphragms. The design factors include diaphragm force amplification factors Ψ and diaphragm shear overstrength factors Ωv. The Ψ factors are applied to the ASCE7‐05 diaphragm design forces to produce diaphragm design strengths aligned to different performance targets. These performance targets are based on diaphragm detailing choices, and include: (i) elastic diaphragm behavior or (ii) limiting inelastic deformation demand on the diaphragm reinforcement (connectors between precast units or reinforcing bars in a topping slab) to within their reliable deformation capacities. The Ωv factors provide overstrength relative to the diaphragm bending strength for capacity protection against shear failure. The analytical study was performed by conducting nonlinear time history analyses of a simple evaluation structure, of which the dimensions and structural properties were varied. The analytical model used in the study is constructed and calibrated on the basis of extensive physical testing. The analytically obtained values of the diaphragm design factors are presented as functions of the geometric and structural properties of the building. The design factors presented here have been verified through evaluation of a set of realistic precast prototype structures. The diaphragm design methodology is currently in the codification process. Copyright © 2015 John Wiley & Sons, Ltd.

A coupled connector element for nonlinear static pushover analysis of precast concrete diaphragms

This paper describes the formulation of a diaphragm connector element developed for use in two-dimensional finite element (2D-FE) modeling of precast concrete diaphragms. The connector elements, composed of assemblages of standard element types readily available in most FE software package libraries, are nonlinear, coupled for shear–tension interaction, enable friction mechanisms, and possess descending branch behavior. Element construction is based on data from full-scale tests of common precast diaphragm connectors. The 2D-FE models have been employed in nonlinear static “pushover” analysis of isolated floor diaphragms to determine diaphragm stiffness, strength, deformation capacity, and limit state sequence. The use of discrete elements to model the precast diaphragm connectors permits the direct evaluation of local force and deformation demands acting on these details. Further, the coupled formulation is adaptable to complex force histories and deformation patterns in the floor diaphragm, thereby permitting the element to respond in realistic fashion. The models, verified for accuracy using large scale testing, are providing crucial information on capacity and limit states for calibrating performance-based design factors for a new seismic design methodology for precast concrete diaphragms.

An evaluation method for precast concrete diaphragm connectors based on structural testing

In the U.S., precast concrete floor diaphragms are a popular form of construction for parking, residential and commercial facilities. Discrete embedded connections bring together large precast concrete panels and transfer vertical and in-plane forces between panels. A consistent experimental procedure is necessary to meet the requirements of performance-based diaphragm design methodologies. In this paper, the authors propose a seismic design methodology for assessing stiffness, strength, and deformation capacity of precast concrete diaphragm embedded connections. They further offer details on developing a test module, loading setup, load histories, instrumentation, data reduction, reporting, and performance categorization.

Analytical Method to Determine the Elastic In-Plane Behavior of Pretopped, Precast Concrete Double-Tee Diaphragms with Discrete Connections

Observed behavior of parking structures, both during seismic events and in subsequent research, indicates that the in-plane behavior of precast concrete double-tee diaphragms may contribute to development of large displacements and affect the structure's seismic performance. The aims of this study were to develop a rigorous analytical basis for practical modeling and determination of elastic in-plane behavior and force distribution among connectors. The elastic in-plane behavior of 10 diaphragm configurations with 4 types of connectors, 2 different connector spacings, and 2 different amounts of chord-member steel was analyzed and compared with that of a monolithic concrete diaphragm. The modeling concepts developed were related to overall connection behavior in the connection zone. They can also be applied to other discretely joined precast concrete structures that exhibit elastic or inelastic behavior mainly in the connection zone.

Integrated Analytical and Experimental Research to Develop a New Seismic Design Methodology for Precast Concrete Diaphragms

AbstractA new seismic diaphragm design methodology has been developed for precast concrete floor diaphragms. The knowledge required to create the design methodology was obtained through an integrated analytical and experimental research project using two Network for Earthquake Engineering Simulation (NEES) equipment sites. The activities of the project involved a sequence of integrated research tasks that systematically developed knowledge about diaphragm behavior from the reinforcement detail level to the structural system level. These tasks included the use of state-of-the-art experimental techniques made possible through the NEES facilities including hybrid simulation and large-scale shake table tests. Such techniques were crucial to the research as the complex behavior of precast diaphragms is not well described by simple analytical models or idealized experiments. Valuable industry oversight in the planning, execution, and technology transfer stages of the project guided the research activities, incl...

Experimental Evaluation of Pretopped Precast Diaphragm Critical Flexure Joint under Seismic Demands

Precast concrete diaphragm seismic response is examined in experimental research integrating model-based simulation with physical testing. The experimental substructure is the diaphragm critical flexural region of a prototype precast parking structure. This region is expected to undergo significant inelastic flexural deformation, while potentially nonductile regions remain elastic on the basis of capacity design rules from an emerging design methodology. The physical test is conducted at half-scale. The test specimen is detailed using diaphragm reinforcement intended to meet deformability requirements. Predetermined displacement histories are applied to the test specimen on the basis of nonlinear transient dynamic analyses of the prototype structure. The loading history is applied by a test fixture capable of simultaneously providing shear, axial, and moment to the joint. Moment strength, stiffness, rotational deformation capacity, and progressive damage are examined under a sequence of increasing intensity earthquakes. Design recommendations are provided.

Precast concrete double-tee connectors, part 2: Shear behavior

Synopsis An experimental study of double-tee, flange-to-flange connections was conducted as part of the PCI/National Science Foundation-funded research effort on the development of a seismic design methodology for precast concrete diaphragms. The research program categorizes the strength and deformation capacity of common double-tee web and chord connectors subjected to in-plane shear or tension loading. This paper presents the experimental results of floor diaphragm connectors subjected to in-plane shear and in-plane shear with tension deformation. The results are compared with expected capacities. The majority of connections subjected to shear with opening restrained exhibited high compression forces coupled with high shear capacity. The application of tension, however, compromised the shear strength. The chord connections tested were found to provide high shear resistance over a limited deformation. Web connectors in topped diaphragm systems provided a high initial shear resistance but returned to the untopped response once the topping reinforcement was lost. The topping slab reinforced with welded-wire reinforcement exhibited brittle shear response with high initial stiffness and strength prior to wire fracture. To improve the connection strength and deformability, recommendations on connector detailing are presented.

Precast concrete double-tee connections, part 1: Tension behavior

An experimental study of flange-to-flange connections of double-tees was conducted as part of the PCI-funded research effort in developing a seismic design methodology for precast concrete diaphragms. The research program categorizes the strength and deformation capacity of common double-tee flange and chord connections under monotonic and cyclic loading. This paper focuses on the tension response of connections compared with design expectations and the contribution they provide in flexural resistance of the diaphragm. The pretopped flange connections were found to resist a moderate tensile force over a large deformation range. Flange connections in topped-diaphragm systems provided a high initial tensile resistance but returned to the untopped response once topping reinforcement failed. The strengths of both chord and flange connections were overpredicted by PCI equations due to brittle modes of weld failure. As a consequence, attention should be paid to field weld alignment; simplified models were developed to more accurately estimate deformation capacity and strength.

Seismic response of parking structures with precast concrete diaphragms

In the 1994 Northridge earthquake in California, parking structures constructed using precast concrete diaphragms appeared to suffer more damage than other structures. The presence of ramps and opening combined with long floor spans led to complex load paths and interdependencies in the flow of lateral forces through the floor diaphragms to shear walls. This paper examines in-plane strength demands, interstory drifts, and force distributions in the diaphragms of parking structures using three-dimensional, inelastic dynamic analyses. The parameters considered in the dynamic analyses included various degrees of diaphragm flexibility, shear wall overstrength, and number of stories. The effects of shear-wall layout and earthquake direction on the seismic response of diaphragms were investigated. The analytical study showed that current code provisions understimate diaphragm force demands and interstory drifts for common structural configurations. It also showed that the current code provisions are insufficient for representing the complex in-plane force paths associated with the shear-wall layout and earthquake direction. Finally, design recommendations to provide sufficient strengh and stiffness for diaphragms were suggested.

Appropriate Overstrength of Shear Reinforcement in Precast Concrete Diaphragms

Current precast concrete diaphragm design may not necessarily protect the diaphragm from a nonductile shear failure in an overload situation. As evidence exists that diaphragms can attract large inertial loads during strong ground motion, emerging design methodologies are aiming to develop the diaphragm flexural strength. However, the performance target desirable or achievable in design may depend on a number of other factors. An analytical study examines the performance of precast diaphragms with different shear strength relative to design (flexural) strength, termed here “shear reinforcement overstrength.” The objective of the study is to determine the required shear reinforcement overstrength in the precast diaphragm to produce certain performance targets. Appropriate shear reinforcement overstrength design factors are proposed in terms of a number of key parameters related to diaphragm geometry and the properties of the diaphragm reinforcing details.

Seismic Design Methodology for Precast Concrete Diaphragms Part 2: Research Program

The Precast/Prestressed Concrete Institute (PCI) is conducting a large area of emphasis project to develop an industry-endorsed comprehensive seismic design methodology for precast concrete floor diaphragms. A multi-university research team from the University of Arizona (UA), Lehigh University (LU), and the University of California San Diego (UCSD) has been selected to perform this collaborative research. An active industry task group is overseeing the planning and execution phases of the research. These groups comprise the DSDM (Diaphragm Seismic Design Methodology) Consortium. The DSDM Consortium research closely integrates finite element analyses of the diaphragm at UA with full-scale reinforcing detail experiments at LU and shaking table system tests at UCSD. The purpose of this and a companion paper, published in the September-October 2005 issue of the PCI JOURNAL, is to outline the foundation for this research and provide context for the technical papers to follow as well as the eventual design methodology. The earlier companion paper described the underlying design philosophy and the resulting design framework that will serve as a basis for the emerging design methodology. This paper focuses on the research program itself, including the integrated research approach, the project's physical scope, and the specific analytical and experimental research activities.