San Francisco, CA, United States
San Francisco, CA, United States

Time filter

Source Type

Yang S.,University of Notre Dame | Mavroeidis G.P.,University of Notre Dame | Ucak A.,Jacobs Associates | Tsopelas P.,National Technical University of Athens
Soil Dynamics and Earthquake Engineering | Year: 2017

High-pass filtering not only removes the low-frequency noise from the near-fault ground motion records, but also eliminates the permanent ground displacement and reduces the dynamic ground displacement. This may considerably influence the calculated seismic response of a spatially extended engineering structure crossing a fault rupture zone. To demonstrate the importance of incorporating permanent ground displacements in the analysis and design of extended structures under specific fault crossing conditions, the dynamic response of a seismically isolated bridge located in the vicinity of a surface fault rupture (“Case A”) or crossing a fault rupture zone (“Case B”) is calculated by utilizing a near-fault ground motion record processed with and without a displacement offset. The seismically isolated bridge considered in this study is a 10-span continuous structure supported by 11 piers, resembling a typical segment of the 2.3 km long Bolu Viaduct 1 located in west-central Turkey. The Lucerne Valley record from the 1992 Mw 7.2 Landers earthquake, which preserves a permanent ground displacement in the fault-parallel direction and exhibits a large velocity pulse in the fault-normal direction, is used as the basis for investigating the effect of high-pass filtering on the dynamic response of the bridge. For the seismically isolated bridge located in the vicinity of the surface fault rupture (“Case A”), the utilization of the high-pass filtered ground motion leads to underestimating the demands of pier top, pier bottom and deck displacements. However, the demands of isolation displacement, isolation permanent displacement and pier drift are almost identical for both the unfiltered and filtered versions of the ground motion record. On the other hand, for the seismically isolated bridge traversed by a fault rupture zone (“Case B”), all response quantities are significantly underestimated when the high-pass filtered ground motion is used. These results, though limited to a single bridge structure and a single ground motion input, clearly indicate the importance of permanent ground displacement on the dynamic response of spatially extended engineering structures crossing fault rupture zones. © 2016 Elsevier Ltd


Stolz J.M.,Jacobs Associates
2012 Proceedings - North American Tunneling, NAT 2012 | Year: 2012

Consider the concept of establishing an optional bid item that compensates the bidder for assuming responsibility for some or all subsurface conditions. The majority of disputes in underground construction tend to focus on ground behavior - a problematic issue since ground behavior is a function of both owner-responsible subsurface conditions and contractor-responsible means and methods. This concept may offer a viable alternative to the contentious, claims-prone process of allocating the degree of responsibility for ground behavior to each party, but it requires input and buy-in from the industry.


Stolz J.M.,Jacobs Associates
North American Tunneling 2010 Proceedings, NAT 2010 | Year: 2010

Bidders read the contract general conditions for projects under consideration for bid before committing to the expense of preparing a bid. This is a smart practice because it oftentimes reveals that the payment terms dictate that the bidder must either add significant financing costs or front-load the bid to obtain a reasonable cash flow. While the industry has made qualitative recommendations to reduce financing costs and discourage unbalanced bids for common contract clauses relating to retention, capped mobilization, the timing of their payment, and the use of equipment mobilization items, there has been no attempt to quantify these savings. By use of a "typical" example tunnel contract, this paper first guides the reader through these payment provisions while quantifying their savings. It then concludes by reinforcing the message that when owners do not consider contractor cash flow in the contract language, they are ultimately either subsidizing significant financing costs or receiving unbalanced bids, and calls for engineer's estimates to have the ability to make these analyses to owners' benefit.


Stolz J.M.,Jacobs Associates
North American Tunneling 2010 Proceedings, NAT 2010 | Year: 2010

There are few industry guidelines that help owners better understand the cost estimates upon which project budgets are based. This paper begins by briefly amplifying the industry consensus that cost estimates for heavy civil and tunnel projects must be based on a "bottom-up" approach. The main focus is on explaining the categories of indirect costs typically used by contractors and their perhaps surprising contribution to overall cost. It then moves on to emphasize the need for an integrated project schedule that quantifies the duration over which these indirect costs are incurred. The paper concludes with a brief examination of and recommendation on the issue of estimating accuracy. These are some of the issues often overlooked when owners review a cost estimate.


Mikola R.G.,Jacobs Associates | Candia G.,University for Development | Sitar N.,University of California at Berkeley
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2016

Observations of the performance of basement walls and retaining structures in recent earthquakes show that failures of basement or deep-excavation walls in earthquakes are rare even if the structures were not designed for the actual magnitude of the earthquake loading. For instance, no significant damage or failures of retaining structures occurred in the recent Wenchuan earthquake in China (2008) or in the subduction earthquakes in Chile (2010) and Japan (2011). To develop a better understanding of the distribution and magnitude of the seismic earth pressures on cantilever retaining structures, a series of centrifuge experiments were performed on model retaining and basement structures with medium dense cohesionless backfill. This paper provides a general overview of the research program and its results. Two sets of centrifuge-scale experiments were carried out on the centrifuge at the Center for Geotechnical Modeling at UC Davis. Three different types of prototype retaining structure were modeled in this research effort as follows: (1) a nondisplacing cross-braced (basement) structure with a stem stiffness of 5.92 × 1010 lb-in.2 per ft width (5.57 × 1005 kN-m2 per m width) and 1.04 × 1010 lb-in.2 per ft width (9.79 × 1004 kN-m2 per m width); (2) a nondisplacing U-shaped cantilever structure with a stem stiffness of 5.92 and 1.04 × 1010 lb-in.2 per ft width (9.79 × 1004 kN-m2 per m width); and (3) a free standing, cantilever retaining wall with a stem stiffness of 2.4 × 1010 lb-in.2 per ft width (2.26 × 1005 kN-m2 per m width). Overall, for the structures examined [i.e., wall heights in the range 6.1-9.15 m (20-30 ft)], the centrifuge data consistently show that the maximum dynamic earth pressure increases with depth and can be reasonably approximated by a triangular distribution. This suggests that the result of the dynamic earth pressure increment acts near 0.33H above the footing as opposed to 0.5-0.6 H recommended by most current design procedures. The current data also suggest that cantilever walls can resist ground accelerations up to 0.4 g if designed with an adequate static factor of safety. © 2016 American Society of Civil Engineers.


Sparks K.,Jacobs Associates
AACE International Transactions | Year: 2012

This paper discusses the role of project cost and schedule control in the planning, contract preparation and execution of a construction project and how proper management of these stages can help manage claims and delays if and when they arise. Starting with the role of the project controls professional during the development phase, this paper will describe how proper cost, schedule, risk management and earned value techniques can be used to properly plan and budget the project. From the planning stage review and support in the preparation of the Division 1 specifications the project controls professional can provide managers with a meaningful baseline and tools to enforce contract requirements. As delay and claim issues occur, proper planned and executed project controls measures will allow owners and contractors to quantify compare these contentious issues.


Gates W.C.B.,Jacobs Associates
47th US Rock Mechanics / Geomechanics Symposium 2013 | Year: 2013

Selection of the appropriate bonding agent for rock anchors is critical to the outcome of the job. The author has observed several projects where rock anchors have failed because the wrong bonding agent was used. Examples include failures in vuggy weak limestone as well as very strong granitic rock. Contractors tend to select resin grouted rock anchors (RGRA) because they are faster, cleaner, and simpler to install, requiring less curing time, a shorter bond zone, one grout cycle, and are economical. The problem is that there are some major disadvantages with RGRA. The resin bonding agent performs poorly in weak, broken and vuggy rock because the resin cartridges require a tight borehole to achieve proper mixing and bonding between the rock and the anchor and don't account for extra voids in the rock around the anchor. Loss of the resin into the voids creates gaps along the anchor and reduces the bond strength. As an alternative, cement grouted rock anchors (CGRA) tend to be more reliable in weak, vuggy, porous rock. Because of the inherent problems with RGRA, the author recommends CGRA because one can achieve a stronger bond in weak, fractured and vuggy rock or poorly drilled holes. The pumped grout tends to flow into the voids around the anchor and form a stronger more secure bond. Copyright 2013 ARMA, American Rock Mechanics Association.


Jacobs A.M.,Jacobs Associates | Cheng D.,Baylor Research Institute
Reviews in Neurological Diseases | Year: 2011

Agents used to treat symptoms of diabetic peripheral neuropathy (DPN) are only palliative, not disease modifying. Although studies of monotherapy with L-methylfolate, methylcobalamin, or pyridoxal 5′-phosphate suggest that each of these bioavailable B vitamins may reverse the pathophysiology and symptoms of DPN, data on the efficacy of this combination therapy are limited. Therefore, we assessed the efficacy of an oral combination of L-methylfolate, methylcobalamin, and pyridoxal 5′-phosphate for improving epidermal nerve fiber density (ENFD) in the lower extremity of patients with DPN. Eleven consecutive patients with type 2 diabetes with symptomatic DPN were assessed for ENFD at the calf by means of skin punch biopsy and then placed on twice daily oral-combination L-methylfolate, methylcobalamin, and pyridoxal 5′-phosphate. After approximately 6 months of treatment, patients underwent follow-up biopsy. At the end of their treatment, 73% of patients showed an increase in calf ENFD, and 82% of patients experienced both reduced frequency and intensity of paresthesias and/or dysesthesias. This preliminary study suggests that combination L-methylfolate, methylcobalamin, and pyridoxal 5′-phosphate increases ENFD in patients with DPN. © 2011 MedReviews®, LLC.


Berry T.,Arup | Wilson S.H.,Jacobs Associates
Proceedings - Rapid Excavation and Tunneling Conference | Year: 2011

In 2002, San Francisco initiated the Water System Improvement Program, the largest public works program ($4.6 billion) in San Francisco history. The 1,280-m-long (4,200-ft), 3.7-m-diameter (12.2-ft) New Crystal Springs Bypass Tunnel is a strategically significant part of the program and involves the installation of a 2.4-m-diameter (8-ft) replacement pipeline to provide seismic reliability to the San Francisco Peninsula's drinking water supply. This paper reviews tunnel design considerations related to Franciscan Complex materials and compares ground conditions anticipated from ground investigations with those encountered on the alignment selected by the contractor. The paper also highlights results from the instrumentation and monitoring of the tunneling operation, including evidence of ground response to tunnel boring machine (TBM) excavation, and reports how the data have been used to validate the geological model. Finally, the paper discusses excavation production data and aspects of TBM design and modifications necessitated by the ground conditions.


Fekete S.,Jacobs Associates | Diederichs M.,Queen's University
International Journal of Rock Mechanics and Mining Sciences | Year: 2013

This paper demonstrates and evaluates 3-dimensional laser scanning (Lidar), in conjunction with block modelling, as a tool for underground rockmass characterization and stability analysis. As a drill-and-blast tunnel advances, Lidar scanning allows for the documentation of the rockmass by collecting creating millions of rock surface point locations in space creating geometric scenes. Databases of structural geology data (joints) can be created by interpreting the "virtual" rockmass. These databases, which include the location of each measurement, can be much more extensive than what is obtained by hand-mapping in traditional geotechnical data collection. The advantages and challenges of Lidar data for underground rockmass evaluation are discussed. The joint database can be subsequently be used in discontinuum modelling in order to evaluate structurally-controlled failure in blocky rockmasses, although not without a number of critical caveats addressed here. These joint system models, either statistically generated or discretely represented, can be far more representative block models than previously possible due to joint position information and a wealth of joint measurements, although a number of pitfalls can occur. The authors present a workflow from data collection and analysis to design outputs for integrating Lidar-derived point-cloud data into rockmass stability modelling. © 2012 Elsevier Ltd.

Loading Jacobs Associates collaborators
Loading Jacobs Associates collaborators