Matthew S. Hoehler

Performance of Suspended Pipes and Their Anchorages During Shake Table Testing of a Seven-Story Building

This paper presents results of shake table tests on pipe systems anchored in a full-scale, seven-story building performed on the Large High-Performance Outdoor Shake Table at the University of California at San Diego on 1 May 2006. The purpose of the tests was to investigate the forces that act on post-installed anchors in buildings during a diverse range of earthquake ground motions. A sound understanding of the force levels and number of cycles is important for developing reliable anchor qualification approaches and seismic design guidelines. The tests also provide data on floor accelerations and acceleration amplification for nonstructural components in buildings during seismic events.

Behavior and Testing of Anchors in Simulated Seismic Cracks

Cast-in-place and post-installed anchors often are used to secure nonstructural elements and to connect new structural elements to existing structures. This study examines the behavior and testing of cast-in-place and post-installed anchors in cracked concrete where the cracks are repeatedly opened and closed. This condition can be decisive for determining the suitability of an anchor for earthquake applications. The results of investigations to establish representative crack cycling conditions for anchors during an earthquake are summarized. New experimental tests with headed studs and four types of post-installed anchors under simulated seismic crack cycling conditions are then presented and discussed. The discussion focuses on the behavior of different anchor failure modes, the influence of the anchor head bearing pressure, and the magnitude of the compression load applied to the concrete member to affect crack closure. These findings can be used as background in developing improved prequalification methods for anchors used in seismic regions.

Behavior of Anchors in Cracked Concrete under Tension Cycling at Near-Ultimate Loads

This study investigates anchor failure mechanisms associated with tension cycling at near-ultimate load levels. Experimental tests with post-installed anchors in cracked concrete were performed. Three types of commercially-available post-installed anchors and one modified anchor were selected to produce distinctly different failure modes. The cracks in the concrete had widths representative of earthquake conditions. The anchors were subjected to monotonic and cyclic tension loads. The results demonstrate that anchors exhibiting failure modes other than anchor steel failure can perform reliably during tension load cycling at near-ultimate levels. The results also indicate that the current definition of ductility in anchor design guidelines must be improved since the current ACI code requirements do not achieve the intended goal of large anchor deformations. These requirements should be coupled with a specified strain length in tension for the anchor in its installed condition.

Experimental Analysis of Steel Beams Subjected to Fire Enhanced by Brillouin Scattering-Based Fiber Optic Sensor Data

This paper presents high temperature measurements using a Brillouin scattering-based fiber optic sensor and the application of the measured temperatures and building code recommended material parameters into enhanced thermomechanical analysis of simply supported steel beams subjected to combined thermal and mechanical loading. The distributed temperature sensor captures detailed, nonuniform temperature distributions that are compared locally with thermocouple measurements with less than 4.7% average difference at 95% confidence level. The simulated strains and deflections are validated using measurements from a second distributed fiber optic (strain) sensor and two linear potentiometers, respectively. The results demonstrate that the temperature-dependent material properties specified in the four investigated building codes lead to strain predictions with less than 13% average error at 95% confidence level and that the Europe building code provided the best predictions. However, the implicit consideration of creep in Europe is insufficient when the beam temperature exceeds 800°C.

Behavior of post-installed anchors tested by stepwise increasing cyclic crack protocols

Cyclic loads are a characteristic feature of actions acting on structures and anchorages during earthquakes. For this reason, seismic qualification of post-installed concrete anchors according to the internationally recognized American Concrete Institute (ACI) standard ACI 355 is based on cyclic load tests. The protocols for these tests, however, have limited scientific basis. Therefore, in the present paper newly-developed test protocols with stepwise-increasing load amplitudes are utilized to more realistically evaluate anchor seismic performance. The study focuses on the load-displacement behavior of common anchor types installed in cracked concrete and subjected to both cyclic tension and cyclic shear actions. The results confirmed robust behavior for anchors loaded in cyclic tension even in the presence of crack widths in the anchorage material larger than currently required by ACI 355. In addition, the critical influence of low cycle fatigue on the performance of anchors loaded in cyclic shear is demonstrated.

Behavior of steel-sheathed shear walls subjected to seismic and fire loads

A series of tests was conducted on six 2.7 m × 3.7 m shear wall specimens consisting of cold-formed steel framing sheathed on one side with sheet steel adhered to gypsum board and on the opposite side with plain gypsum board. The specimens were subjected to various sequences of simulated seismic shear deformation and fire exposure to study the influence of multi-hazard interactions on the lateral load resistance of the walls. The test program was designed to complement a parallel effort at the University of California, San Diego to investigate a six-story building subjected to earthquakes and fires. The test results reported here indicate that the fire exposure caused a shift in the failure mode of the walls from local buckling of the sheet steel in cases without fire exposure, to global buckling of the sheet steel with an accompanying 35 % reduction in lateral load capacity after the wall had been exposed to fire. This behavior appears to be predictable, which is encouraging from the standpoint of residual lateral load capacity under these severe multi-hazard actions.

Application of Blue Laser Triangulation Sensors for Displacement Measurement Through Fire

This paper explores the use of blue laser triangulation sensors to measure displacement of a target located behind or in the close proximity of natural gas diffusion flames. This measurement is critical for providing high-quality data in structural fire tests. The position of the laser relative to the flame envelope can significantly affect the measurement scatter, but has little influence on the mean values. We observe that the measurement scatter is normally distributed and increases linearly with the distance of the target from the flame along the beam path. Based on these observations, we demonstrate how time-averaging can be used to achieve a standard uncertainty associated with the displacement error of less than 0.1 mm, which is typically sufficient for structural fire testing applications. Measurements with the investigated blue laser sensors were not impeded by the thermal radiation emitted from the flame or the soot generated from the relatively clean-burning natural gas.

Ceiling Anchorage Loads during Shake Table Tests of a Full-Scale Five-Story Building

This paper documents tests conducted to assess anchor loading characteristics and distributions over a suspended ceiling before, during, and after a series of simulated earthquakes. Miniature force-measurement devices were installed on a 4.5 by 6.5 m section of gypsum board ceiling located in a full-scale five-story building. The building was subjected to a series of four scaled earthquakes until failure of the ceiling occurred. The test results show that the ceiling-to-slab acceleration amplification was a factor of about 6.4 for horizontal accelerations and 15.0 for vertical acceleration immediately prior to failure of the ceiling. Variation of the peak axial anchor forces across the ceiling under earthquake loading was significant; the maxima exceed the mean value by a factor of up to 3.8 times. Rainflow counting of axial anchor load cycles is used to provide cycling demand for both the linear and nonlinear response of the ceiling.

Temperature measurement and damage detection in concrete beams exposed to fire using PPP-BOTDA based fiber optic sensors

In this study, distributed fiber optic sensors based on pulse pre-pump Brillouin optical time domain analysis (PPP-BODTA) are characterized and deployed to measure spatially-distributed temperatures in reinforced concrete specimens exposed to fire. Four beams were tested to failure in a natural gas fueled compartment fire, each instrumented with one fused silica, single-mode optical fiber as a distributed sensor and four thermocouples. Prior to concrete cracking, the distributed temperature was validated at locations of the thermocouples by a relative difference of less than 9 %. The cracks in concrete can be identified as sharp peaks in the temperature distribution since the cracks are locally filled with hot air. Concrete cracking did not affect the sensitivity of the distributed sensor but concrete spalling broke the optical fiber loop required for PPP-BOTDA measurements.

DUCTILITY REQUIREMENTS FOR THE ANCHORAGE OF NONSTRUCTURAL COMPONENTS

The issuance and widespread adoption of the current suite of U.S. codes and standards (2006 IBC, ASCE 7-05, ACI 318-05) addressing the anchorage of nonstructural components for earthquake forces raises several questions regarding requirements and expectations for the ductility of the anchorage. This presentation explores the implications of the current code requirements and offers a realistic assessment of what is achievable in the context of structural practice and anchor design.