Construction In Seismic Regions Research Articles

Connections for Integral Jointless Bridges in Seismic Regions Suitable for Accelerated Bridge Construction

Prefabricated jointless bridges consisting of pretensioned girders, posttensioned spliced girders, trapezoidal open box girders, and other types of superstructure members are often used for accelerated bridge construction. Connections in precast concrete substructures are typically made at the beam–column and column–foundation interfaces to facilitate fabrication and transportation. However, for structures in seismic regions, those interfaces represent locations of high moments and shears and large inelastic cyclic strain reversals. Jointless bridge superstructures are constructed to work integrally with the abutments. Movements due to creep, shrinkage, and temperature changes are accommodated by using flexible bearings or foundation and through incorporating relief joints at the ends of the approach slabs. In addition to reduced maintenance costs, other advantages of jointless bridges include improved structural integrity, reliability and redundancy, improved long-term serviceability, improved riding surface, reduced initial cost, and improved aesthetics. In recent times, jointless bridges have been built in seismically sensitive areas. Developing connections that can accommodate inelastic cyclic deformations and are readily constructible is the primary challenge for accelerated bridge construction in seismic regions. The AASHTO load and resistance factor design specifications do not explicitly address jointless precast, pretensioned, or posttensioned elements. The seismic design and detailing, accomplished research, and construction practices of jointless bridges, and implementation of a precast concrete bridge bent system that is intended to meet all those challenges, are presented. This paper attempts to capture the state of practice of jointless continuous bridges in seismic regions.

FRP-confined concrete filled PVC tubes: A new design concept for ductile column construction in seismic regions

In their recent work Fakharifar and Chen (2016) [1] have introduced and validated a new ductile design concept of confined concrete-filled polyvinyl-chloride tubular (CCFPT) columns through experimental and analytical studies. Confinement was provided with the use of a polyvinyl-chloride (PVC) tube and fiber-reinforced polymer (FRP) wrappings or FRP with a sandwiched layer of foam to enhance impact energy reduction due to potential FRP rupture and PVC fracture. In the present paper, additional flexural tests on CCFPT columns were undertaken to further investigate the structural behavior of the proposed system for column construction in seismic regions. Axial and flexural behavior of CCFPT columns was investigated with compressive and flexural tests, respectively, and compared with those of their corresponding concrete-filled polyvinyl-chloride tubular (CFPT) and FRP-wrapped (FW) columns. Test results obtained from 152×305mm (6×12in.) stub columns under axial loads and 152×1524mm (6×60in.) flexural beams under four-point loads indicated that the CCFPT columns can significantly enhance strength over the CFPT columns and enhance ductility over the FW columns. The transverse confining pressure from FRP wrapping and the interface property between the FRP and PVC proved critical in CCFPT design. Furthermore, the idea of introducing a cushioning foam layer between FRP layers and PVC to lessen the brittleness of FRP rupture in seismic regions proved effective.

Quasi-static cyclic testing of emulative cast-in-place connections for Accelerated Bridge Construction in seismic regions

This paper presents findings from the first phase of testing at the University of Canterbury on seismic performance of emulative connections for Accelerated Bridge Construction (ABC) in regions of moderate to high seismicity. Emulative connections between precast concrete elements aim to target similar seismic behaviour as traditional ductile monolithic construction. The emulative solution in this research is called “High Damage Connection” (HDC). HDCs intend to achieve similar levels of seismic performance and ductility in a precast column as that can be expected of a monolithic one. HDC relies on formation of plastic hinges in the precast column during a design level earthquake to emulate monolithic ductile behaviour. Two types of HDCs, the grouted duct connection and member socket connection, were investigated in this research. Four half-scale precast segmental columns were constructed. Two columns featured grouted duct connections as the primary connection type. The other two columns used member socket connections. For a better understanding of the connection response under severe lateral loading, both uniaxial and biaxial testing of the columns was carried out. In this paper, an introduction to each connection type followed by design procedure, detailing considerations and construction methodology are explained in detail. Testing results and observations of seismic performance for each connection are thoroughly presented. The research concludes that High Damage Connections have good potential for ABC in regions of moderate to high seismicity. The connections that were tested achieved good levels of energy dissipation and ductility with similar performance to conventional monolithic connections.

RETRACTED ARTICLE: On the seismic performance of bamboo structure

While the earthquake resistant building design and construction code has been developed in sophisticated national/city level, the implementation at the local level has been more of an exception than the rule. Other than concrete and steel, one such material that can be used in construction in the seismic zone area of the developing countries like India, especially in the northeast states, is bamboo, where bamboo is available in abundant. Bamboo’s light weight and relative flexibility make it a particularly attractive alternative for residential construction in seismic regions. Compared on a mass-per-volume basis to concrete, steel and wood, bamboo is second to concrete for strength, and ranks first for stiffness. As strong as mild steel with the compression strength of concrete, amazingly, one inch of bamboo can hold up to 7 1/2 tons of weight. This present study is an attempt to implement bamboo construction in Manipur which is regarded as one of the most seismically active regions worldwide. In this work, a bamboo housing system and a reinforced concrete frame structural system was modeled using finite element analysis program SAP, considering the model structures to be taken from the types of building that is built in Manipur. A parametric study is conducted to investigate the seismic performance of the structures and El-Centro Earthquake and Kobe Earthquake recorded excitation are used for input in the dynamic analysis on the models. The study has revealed that the bamboo structures are performing better in earthquake than the commonly built RC residential building. The behavior of the bamboo structure modeled in this present study gives an opportunity to accept bamboo as a construction material in seismic zone areas.

Probabilistic Robustness Assessment of Pre-Northridge Steel Moment Resisting Frames

This paper investigates the robustness of moment-resisting steel frames that are typical of building construction in seismic regions before the 1994 Northridge earthquake against progressive (disproportionate) collapse. Uncertainties in the collapse demands and the resisting capacities of the connections in the frames are modeled probabilistically. The dominant connection failure mode, which involves fracture of the weld connecting the beam and column flanges under scenarios involving sudden column loss, is developed using a J-integral formulation of fracture demand and is characterized probabilistically. The connection behavior model is validated using connection test data from the SAC Project on steel frames conducted following the Northridge earthquake. The robustness of two three-story steel frames designed in the SAC Project is assessed by utilizing (a) the requirements in the new Unified Facilities Criteria (UFC), and (b) a system reliability analysis. This analysis reveals that steel moment frames with connections similar to those found in pre-Northridge building construction may not meet the UFC requirements for general structural integrity following notional column removal.

Shear and Flexural Behavior of Lightweight Concrete Bridge Columns in Seismic Regions

This paper describes research related to the use of lightweight concrete for bridge column construction in seismic regions. Of interest is the behavior of columns dominated by shear as well as those dominated by flexure. A series of large-scale experimental tests was performed to assess the response of reinforced lightweight concrete columns in the inelastic range. Results indicate that a reduction in shear and flexural strength is appropriate for lightweight concrete, while displacement capacity and energy dissipation are not affected in a significant manner.

Moment Resistant Connections in Precast Concrete Frames for Seismic Regions

The concept of relocating the plastic hinge region of precast concrete frames for construction in seismic regions is examined. Five beam-to-column subassemblies were tested under simulated earthquake-type loading. The connections included steel plates or angles embedded in the columns and beams which would facilitate field erection. The column axial load was held constant during the test while the free end of the beam was subjected to reversed cyclic displacements. The failure modes, strength and ductility of the test specimens using various connection details are compared. It is concluded that properly designed connections with relocated plastic hinges can perform in a satisfactory manner. The reduced welding requirements for these details result in improved economy of construction.

Suggestions on improving the section “Construction in Seismic Regions” of SNiP II-A.12-69

Suggestions on improving the section “Construction in Seismic Regions” of SNiP II-A.12-69

Conference on seismology and construction in seismic regions

Conference on seismology and construction in seismic regions