Browsing by Subject "Earthquake resistant design"

Now showing 1 - 7 of 7

Analysis of the effect of hysteretic relationships in beam-column connections on the earthquake response of precast reinforced concrete frame systems
(1993) Brewer, Lori Wilson, 1968-; Not available
Increased Single-Lift Thicknesses for Unbound Aggregate Base Courses
(1998-10) Allen, John J.; Bueno, Jaime L.; Kalinski, Michael E.; Myers, Michael L.; Stokoe, Kenneth H.
A study was conducted to evaluate the feasibility of compacting unbound aggregate base courses in thicker lifts than currently permitted by state departments of transportation (DOTs). At present, the majority of states allow a maximum lift thickness of 8 inches or less. This project constructed and tested full-scale test sections using a variety of material types. Two test pads were constructed in an aggregate quarry in Texas utilizing crushed limestone. Three crushed granite test sections were built as part of a road widening project in Georgia, and two test pads were constructed of uncrushed and partially crushed gravel with loess fines at a gravel production facility near Memphis, Tennessee. Single-lift thicknesses varied from 6 inches to 21 inches. Moisture contents and densities were evaluated using the Nuclear Density Gauge (NDG). Nondestructive seismic testing, using the Spectral-Analysis-of-Surface-Waves (SASW) technique, was used to evaluate stiffness profiles within the compacted lifts. Cyclic plate load tests were accomplished by means of the Rolling Dynamic Deflectometer (RDD), modified for this static application. Results showed that compaction targets could be attained for lifts up to 21 inches thick. Density and stiffness results for 13-inch thick lifts in the Georgia tests were equal to, or better than, the results for the base placed in two lifts, a 7-inch lift followed by a 6-inch lift. Higher moisture contents during compaction yielded lower shear wave velocity and Young’s modulus values. Seismic results show that the upper 3 inches of the final test pads had lower stiffness values, presumably from lower effective stresses near the surface and possibly from some disturbance caused by the compaction equipment. This zone of lower stiffness and slightly less compaction is less evident in the density measurements.
Prediction of Working Load Displacements Under Plate Loading Tests from Seismic Stiffness Measurements
(1998-10) Myers, Michael L.; Stokoe, Kenneth H.; Allen, John J.
A study was conducted to evaluate the feasibility of compacting unbound base courses in thicker lifts than currently permitted by state departments of transportation (DOTs). At present, the majority of states allow a maximum lift thickness of 8 inches or less. This project constructed and tested full-scale test section using a variety of material types. Two test pads were constructed in an aggregate quarry in Texas utilizing crushed limestone. Three crushed granite test sections were built as part of a road widening project in Georgia, and two test pads were constructed of uncrushed and partially crushed gravel with loess fines at a gravel production facility near Memphis, Tennessee. Single-lift thicknesses varied from 6 inches to 21 inches. Moisture contents and densities were evaluated using the Nuclear Density Gauge (NDG). Nondestructive seismic testing, using the Spectral-Analysis-of Surface-Waves (SASW) technique, was used to evaluate stiffness profiles within the compacted lifts. Plate load tests were conducted on the surface of the crushed limestone test pads by means of the Rolling Dynamic Deflectometer specially modified for this fixed site application. Low frequency cyclic loads were applied to determine axial stiffness under transient working loads of varying magnitude. The base courses were tested at to moisture contents. The results were evaluated and compared with small strain seismic tests result. Strain amplitudes in the plate load tests led to a 5% to 25% reduction in measured stiffness as compared to the seismic results.
Seismic performanc of link-to-column connections in steel eccentrically braced frames
(2004) Okazaki, Taichiro; Engelhardt, Michael D.
This dissertation describes a research program on the seismic performance of link-to-column connections in steel eccentrically braced frames (EBFs). Since the 1970’s, EBFs have been accepted as a high performing steel building system for seismic regions. Many of the same design, detailing, and construction features that contributed to the widespread damage in welded moment connections in the 1994 Northridge Earthquake are present in link-to-column connections in EBFs. However, little research has previously been conducted on link-to-column connections. The research program combined an experimental investigation involving large-scale cyclic loading tests, and an analytical study including detailed finite element simulations to study link-to-column connections. A total of sixteen large-scale link-column specimens were tested in the experimental study. Four different connection types with varying configuration and welding details were tested. Each of the four connection types was tested with a variety of link lengths to consider a wide range of force and deformation environment at the link-to-column connection. The specimens representing the pre-Northridge practice failed after developing only half of the inelastic link rotation required in the building code provisions. Implementing improvements in welding was beneficial, but this alone was not nearly sufficient to improve the connection performance to the required level. Improved connection details developed for moment connections did not necessarily provide good performance for link-to-column connections. The force and deformation demand at EBF link-to-column connections were found to be significantly more severe than at moment connections. The local stress and strain environment predicted by finite element simulations correlated well with the fracture behavior observed in the test specimens. The finite element simulations also agreed with the experimental observations in that fracture of the link flange near the groove weld connecting to the column flange is a major concern for links of all practical lengths. The findings from this research suggest that until further research is available, EBF arrangements with links attached to columns should be avoided.
Seismic strengthening by providing structural diaphragm
(2006) Wang, Renjun; Jirsa, J. O. (James Otis); Wood, Sharon L.
There are a large number of precast frame buildings used in Turkey for industrial facilities. One-story warehouses are the most common structural configurations. Because there was little redundancy in the lateral load resisting system, many precast buildings were damaged beyond repair during the 1999 earthquakes in Turkey. In the present study, a rehabilitation scheme is proposed to add a structural diaphragm at the roof level by adding diagonal bracing. With the diaphragm action developed, the lateral forces can be transmitted among the cantilever columns, and to the vertical diagonal braces on the periphery, thus the seismic performance can be enhanced. An analysis method is also developed for the rehabilitation design.
A Study on the Feasibility of Compacting Unbound Graded Aggregate Base Courses in Thicker Lifts Than Presently Allowed by State Departments of Transportation
(1998-10) Bueno, Jaime Luis; Stokoe, Kenneth H.; Allen, John J.
A study was conducted to evaluate the feasibility of compacting unbound aggregates base courses in thicker lifts than currently permitted by state departments of transportation (DOTs). At present, the majority of states allow a maximum lift thickness of 8 inches or less. This project constructed and tested full-scale test sections using a variety of materials types. Two test pads were constructed in an aggregate quarry in Texas utilizing crushed limestone, and three crushed granite test sections were built as part of a road widening project in Georgia. Single-lift thickness varied from 6 inches to 21 inches. Moisture contents and densities were evaluated using the Nuclear Density Gauge (NDG). Nondestructive seismic testing, using the Spectral-Analysis-of Surface-Waves (SASW) techniques, was used to evaluate stiffness profiles within the compacted lifts. Results showed that compaction targets could be attained for lifts up to 21 inches thick. Density and stiffness results for 13-inch thick lifts in the Georgia tests were equal to, or better than, the results for the base placed in two lifts, a 7-inch lift followed by a 6-inch lift. Higher moisture contents during compaction yielded lower shear wave velocity and Young’s modulus values. Seismic results show that the upper 3 inches of the final test pads had lower stiffness values, presumably from lower effective stresses near the surface and possibly from some disturbance caused by the compaction equipment. This zone of lower stiffness and slightly less compaction is less evident in the density measurements.
Tension bolt behavior in moment connections for seismic applications
(1996) Ulloa Barbaran, Fernando Valentin; Yura, J. A.
Recent seismic events such as the Northridge earthquake have left behind, along with destruction serious doubts about the performance of the welded moment connection, until now the most popular and reliable steel beam-column connection. A careful study of the structures damaged by these earthquakes, has established that welded connections mainly failed due to fracture along the full penetration groove weld. This rather unexpected behavior of this type of connection has prompted additional research on welded connections and research on other type of connections, i.e., bolted connections. The former has led to some recommendations aimed mainly at strengthening of the connection by making use of additional stiffeners and new welding techniques. All of this has resulted in an increase of the overall cost of this type of connection, in such a way that the previously more expensive bolted connection has become a viable alternative to the traditional welded connection. All bolted beam-column connections are controlled by the behavior of the structural members connecting the beam flange to the column flange, i.e. Tees, angles. High strength bolts are used as the connectors. These Tees generally are designed as hanger-type connections. While extensive work on hanger-type connections subjected to monotonic loading has been reported, very limited work has been done on these type of connections subjected to cyclic loading. A set of tests involving five full scale specimens, all bolted beam-column connections, were performed at the University of Texas at Austin. The goal of these tests was to study the behavior of this type of beam-column connection when subjected to cyclic loading and devising seismic design guidelines and recommendations for a proper design of this type of connection