Stochastic Database Cracking: Towards Robust Adaptive Indexing in Main-Memory Column-Stores

Modern business applications and scientific databases call for inherently dynamic data storage environments. Such environments are characterized by two challenging features: (a) they have little idle system time to devote on physical design; and (b) there is little, if any, a priori workload knowledge, while the query and data workload keeps changing dynamically. In such environments, traditional approaches to index building and maintenance cannot apply. Database cracking has been proposed as a solution that allows on-the-fly physical data reorganization, as a collateral effect of query processing. Cracking aims to continuously and automatically adapt indexes to the workload at hand, without human intervention. Indexes are built incrementally, adaptively, and on demand. Nevertheless, as we show, existing adaptive indexing methods fail to deliver workload-robustness; they perform much better with random workloads than with others. This frailty derives from the inelasticity with which these approaches interpret each query as a hint on how data should be stored. Current cracking schemes blindly reorganize the data within each query's range, even if that results into successive expensive operations with minimal indexing benefit. In this paper, we introduce stochastic cracking, a significantly more resilient approach to adaptive indexing. Stochastic cracking also uses each query as a hint on how to reorganize data, but not blindly so; it gains resilience and avoids performance bottlenecks by deliberately applying certain arbitrary choices in its decision-making. Thereby, we bring adaptive indexing forward to a mature formulation that confers the workload-robustness previous approaches lacked. Our extensive experimental study verifies that stochastic cracking maintains the desired properties of original database cracking while at the same time it performs well with diverse realistic workloads.Comment: VLDB201

Cracking KD-Tree: The first multidimensional adaptive indexing

Workload-aware physical data access structures are crucial to achieve short response time with (exploratory) data analysis tasks as commonly required for Big Data and Data Science applications. Recently proposed techniques such as automatic index advisers (for a priori known static workloads) and query-driven adaptive incremental indexing (for a priori unknown dynamic workloads) form the state-of-the-art to build single-dimensional indexes for single-attribute query predicates. However, similar techniques for more demanding multi-attribute query predicates, which are vital for any data analysis task, have not been proposed, yet. In this paper, we present our on-going work on a new set of workload-adaptive indexing techniques that focus on creating multidimensional indexes. We present our proof-of-concept, the Cracking KD-Tree, an adaptive indexing approach that generates a KD-Tree based on multidimensional range query predicates. It works by incrementally creating partial multidimensional indexes as a by-product of query processing. The indexes are produced only on those parts of the data that are accessed, and their creation cost is effectively distributed across a stream of queries. Experimental results show that the Cracking KD-Tree is three times faster than creating a full KD-Tree, one order of magnitude faster than executing full scans and two orders of magnitude faster than using uni-dimensional full or adaptive indexes on multiple columns

Computational Modeling and Simulations of Condition Deterioration to Enhance Asphalt Highway Pavement Design and Asset Management

A nation’s economy and prosperity depend on an efficient and safe transportation network for public mobility and freight transportation. A country’s road network is recognized as one of the largest public infrastructure assets. About 93 percent of 2.6 million miles of paved roads and highways in the United States (U.S.) are surfaced with asphalt. Longitudinal roughness, pavement cracking, potholes, and rutting are the major reasons for rehabilitation of asphalt roads. Billions of dollars are required annually for the maintenance and rehabilitation of road networks. If timely maintenance and rehabilitation are not performed, the pavement damages inflicted by heavy traffic repetitions and environmental impacts may lead to life threatening condition for road users. This research is focused on asphalt pavement condition deterioration progression modeling and computational simulations of uncracked and cracked asphalt pavement-subgrade models. The research objectives are to (1) evaluate and enhance asphalt pavement condition deterioration prediction models, (2) evaluate modulus backcalculation approaches for characterizing asphalt pavement layers of selected test sections, (3) develop three dimensional-finite element (3D-FE) asphalt pavement models and study impacts of cracking on pavement structural responses, and (4) implement pavement condition deterioration models for improved structural design and asset management of asphalt highway pavements. The historical asphalt pavement database records of the Long-Term Pavement Performance (LTPP) research program were used to develop asphalt pavement condition deterioration progression models, considering LTPP regions and maintenance and rehabilitation history. The enhanced condition deterioration prediction equations of the International Roughness Index (IRI), rutting, and cracking distresses were developed and evaluated in this research for LTPP datasets of 2,588 for IRI, 214 for rutting, and 2,240 for cracking. The LTPP regions and major maintenance intervention criteria were comfactors considered in all multiple regression equations. The IRI prediction equation also considered the IRI measurement location factor. Additionally, the rutting prediction equation includes additional factors of in situ modulus of pavement layers and base layer type. In comparison, the U.S. national mechanistic empirical pavement design guide (MEPDG) performance prediction models do not include maintenance and rehabilitation and climatic factors which present major limitations of the MEPDG method of pavement thickness design. Both regression analysis and Artificial Neural Network (ANN) analysis methods were used and the results were compared. The IRI multiple regression equation shows R of 0.633, which is slightly lower compared to the ANN IRI model’s R of 0.717. The IRI predictions using the enhanced multiple regression equation are comparable with the ANN results for verification data sets. The prediction equations from multiple regression modeling and ANN modeling of rutting distress show high R values above 0.93 and 0.94, respectively, and reasonably accurate result of model database and verification section. These model equations have got higher R value compared to the MEPDG’s R value. A new cracking model namely Unified Cracking Index (UCI) was developed in this research by combining all crack types which is not available in the MEPDG. The overall UCI combines the densities (% crack area per total area) of the alligator, block, longitudinal, and transverse cracking types. This approach is practical and easy to implement with intervention criteria of maintenance and rehabilitation for life-cycle asset management of asphalt highway pavements. The UCI equations using multiple regression for log transformation and using sigmoidal transformation for the model database shows the correlation, R, of 0.551 and 0.511 respectively, with 19.5 and 4.1 percent errors in predictions compared to the measured LTPP data. In comparison, the ANN model for UCI shosignificant improvements in R value (0.707) with 14.6% error. It also shohigh R value (0.861) and low error for the verification data sets. The MEPDG method includes separate models of alligator crack, longitudinal crack (defined as fatigue induced crack in the MEPDG), and transverse crack. In comparison, this research developed prediction equations not only for alligator, longitudinal, and transverse cracks but for block crack too. Individual ANN model of cracking (alligator, block, longitudinal, transverse) also shoreasonably accurate results. In situ modulus values of existing pavements are other important material inputs for pavement structural response analysis of overlay thickness design. Several modulus backcalculation software, based on the layer elastic static analysis theory, were evaluated in this research for selected LTPP highway sections. The comparisons indicated that the backcalculated modulus values in the LTPP database were generally unreasonable using the EVERCALC 5.0 software. Overall, the backcalculated modulus values using BAKFAA 2.0 and PEDD/UMPED were generally reasonable for all pavement layers. It was also shown that the thickness design of longer lasting pavement performance depends on seasonal layer modulus values considering extreme weather and climate attribute. In order to create a structural response database for pavement-subgrade subjected to design truck axle load, the 3D-FE models of uncracked and cracked asphalt pavement layer were developed using the LS-DYNA finite element software. The structural responses such as surface deflections, stresses and strains at different depths in the pavement-subgrade model were analyzed for critical locations. A full factorial experiment for six independent variables at two levels was designed, and the simulations for 64 treatment combinations were executed for the uncracked model. The results of the 3D-FE models shocomparable results with previous studies using the LS-DYNA software and the outputs of the GAMES linear elastic program. An extended analysis was conducted on the cracked model to study the effect of full depth cracked on effective viasphalt modulus values. Based on the full-depth cracked 3D-FE model results, low-level modulus of weak pavements shoa higher reduction of 81.0 % in the asphalt modulus compared to the compared to the asphalt modulus of the uncracked 3D-FE model, while the high-level modulus and thick pavement shoa low reduction of 13.5 % in the asphalt modulus of the uncracked pavement model. The development of the enhanced pavement condition prediction equations provide significant improvements over the MEPDG method, such as consideration of maintenance and rehabilitation history and climatic regions, using larger number of LTPP datasets, compared to model data sets used in the MEPDG. Therefore, the developed equations are more appropriate for the pavement structural design and asset management of asphalt highways. This implementation will contribute towards longer-lasting asphalt highway pavement assets to serve the public, improve safety, support efficient supply chain and economic growth

Bond performance of recycled aggregate concrete

In recent decades, engineers have sought a more sustainable method to dispose of concrete construction and demolition waste. One solution is to crush this waste concrete into a usable gradation for new concrete mixes. This not only reduces the amount of waste entering landfills but also alleviates the burden on existing sources of quality natural concrete aggregates. The objective of this study was to determine to effect of replacing coarse natural aggregates for recycled concrete aggregates (RCA) on the bond strength between deformed mild reinforcing steel and surrounding concrete. Two different RCA replacement levels were considered, 50% and 100%, and were compared to a standard Missouri Department of Transportation (MoDOT) mix design. All RCAs used were crushed from laboratory cured beams of the same MoDOT mix design containing 1 in. Potosi Dolomite crushed stone. To evaluate bond strength, 18 direct pull-out specimens were tested with both #4 (No. 13) and #6 (No. 19) reinforcing bars and 9 full-scale beam specimens were tested with non-confined contact lap splices located at mid-span. The construction and test procedure of the direct pull-out specimens was based on RILEM 7-II-128. The full-scale beam splice specimens were based on a non-standard test procedure that is considered to be the most realistic stress state response for bond. Analysis of the test data indicates that replacing more than 50% of coarse natural aggregates results in diminished bond strength over concrete containing only virgin natural aggregates. This result suggests that the existing equation for development and splice length as reported in ACI 318 may require additional modification factors to account for the diminished bond strength associated with replacement of coarse virgin aggregates with RCA. --Abstract, page iii

INVESTIGATION OF EARLY-AGE CRACKING IN CONCRETE BRIDGE CURBS

In recent years a number of newly constructed curbs on New Hampshire Department of Transportation (NHDOT) single-span roadway bridges have suffered from cracking within one year after placement. The cracking that occurs in bridge curbs may provide easy ingress of water and chloride ions into the curb which could accelerate deterioration. An additional concern is that cracks in the curb could extend into the bridge deck. Ideally, bridge curbs and bridge decks are replaced at the same time in an effort to reduce the frequency of lane closures and frequency of mobilizing a crew to perform repeated rehabilitation. Potential accelerated deterioration related to early-age cracking would likely mean that curb and deck replacement would not be done at the same time, leading to increased agency costs and inconvenience to the driving public. This thesis focuses on the survey and analysis of data collected at several bridges in an effort to find ways to reduce cracking in bridge curbs. Seventeen existing bridges that had been placed in the past eleven years, in addition to six bridges placed during the study, were examined for curb cracking. Four of the bridges had variables applied to one of the curbs to try and identify which items could contribute to crack reduction. Results indicate that longer bridges experience a greater amount of cracking per foot than shorter bridges. There is also a relationship between the amount of cracking and location on the curb relative to the ends of the curb. Pairs of curbs suggest longer wet cure durations and lower cementitious content PCC mixes reduce cracking

CORROSION ACTIVITY IN PRECAST CONCRETE ELEMENTS AND CEMENTITIOUS CLOSURE POURS

The use of prefabricated elements in the construction of highway bridges has been a common practice in the United States since 1950s. Precast concrete adjacent box beam girder bridges are quite popular given that the precast elements not only have structural capacity to span across the supports, but also form the bridge deck. These bridges have generally performed well during the initial years after construction, but recent failures in Pennsylvania and Indiana have aroused a nationwide alarm to investigate the causes of failure and find solutions to repair these bridges or develop design for new replacement bridges. It was found that the stressed and non-stressed embedded reinforcements were severely corroded due to the ingress of chloride ions in the bridge deck through the surface cracks occurring within the closure pours (shear key) and at the interface of the joints between the precast elements and the shear key. The primary objective of this research is to find an easy and reliable technique to detect the initiation of corrosion in embedded rebar with minimal disturbance to the moving traffic and to investigate the condition of the rebar (active or passive with respect to corrosion) embedded in Ultra High Performance Fiber Reinforced Concrete (UHPFRC) so that precautionary measures and maintenance can be applied before the failure of more in-service bridges. The experimental investigation considered three different samples; ASTM modified G 109 samples (laboratory samples) which served as a control type specimen and large uncracked and cracked specimens (field samples) which served as an actual prototype of a bridge deck. These samples were exposed to 3% of NaCl solution in the wet condition for duration of two weeks in alternate cycles of wet and dry period to accelerate the corrosion process. Half-cell potential (HCP) tests and linear polarization resistance (LPR) tests were carried out on all the samples. HCP test was able to detect the accurate location of corrosion by measuring the corrosion potential in the rebar and LPR test was able to confirm the active or passive state of the rebar by measuring the corrosion current in the rebar. The results of both these tests were validated by observing the physical condition of the rebar which were obtained from cores extracted from each sample types. It was found that rebar were mainly corroded at the interface of the joints between two different materials and areas of the samples which were cracked from the bottom in case of cracked samples. The corrosion of rebar was most prominently observed in the UHPFRC with PVA fibers even at places without joints and cracks. More intensive investigation is needed which will require more time and applications of more detail electro-chemical techniques to arrive at a more confident conclusion

Fatigue and fracture of tubulars containing large cracks

This thesis presents an investigation into the performance of offshore tubular components containing large defects. The significance of the residual strength of cracked tubular members is considered with respect to inspection and maintenance of structural integrity. A series of nine destructive static strength tests were performed on full-scale precracked tubular welded T and Y-joints manufactured from a weldable high strength steel (Superelso 702), which is utilised in the construction of offshore Jack-Up platforms. All specimens had at least one through-thickness fatigue crack at the weld toe, from a previous fatigue-testing programme. Static strength tests on four large tubular sections manufactured from BS7191 355D were also carried out. The specimens contained either a through-thickness or a part- through-thickness defect. A novel digital photogrammetry technique was utilised to maximise the data collection from the destructive tests. The method is capable of the quantification of three-dimensional displacements, which subsequently allowed for a better understanding of the behaviour of the specimens during the tests. A fracture mechanics study of tubular components containing large cracks is presented. The limited number of stress intensity factor (SIF) solutions for cracks in tubular sections are considered and a new SIF solution for tubular T-joints, containing through-thickness cracks, under axial loading is provided. The method is based on the SIF at the crack tip and the non-uniform stress distribution present in an axially loaded tubular T-joint. The information has been integrated into the safety evaluation of all specimens using a failure assessment diagram (FAD) procedure. Finally, the local and the global responses of a structure to the presence of a large defect are reviewed. The importance of redundancy and multiple load paths are stressed and possible repair and maintenance options are considered

Transactional support for adaptive indexing

Adaptive indexing initializes and optimizes indexes incrementally, as a side effect of query processing. The goal is to achieve the benefits of indexes while hiding or minimizing the costs of index creation. However, index-optimizing side effects seem to turn read-only queries into update transactions that might, for example, create lock contention. This paper studies concurrency contr

Seismic In-Plane Response of Reinforced Concrete Frames with Masonry Infill Walls

Field data gathered after destructive earthquakes indicate that infill walls interact with reinforced concrete (RC) frames in buildings during an earthquake and could cause failure mechanism different than what the frames are originally designed for. A new method to identify the failure modes of RC frames with infill walls is developed. The method requires only the simple geometric and material properties of the elements involved in the frame- wall assembly. The approach checks various possible failure mechanisms, including those that may evolve depending on how the infill wall may fail during strong shaking, for example, the dynamically evolved captive column mode. A new hysteresis model is developed for RC frames with infill walls to investigate the ultimate damage state given a ground motion. The hysteresis model is compared with data from experiments by other researchers. The approach and hysteresis model result in estimates that agree with the failure modes observed in the experiments. The ability of finite element modeling is investigated to predict the performance of RC frames with infill walls. The techniques used to simulate materials and interfaces to estimate the cyclic in-plane response of RC frames infilled with masonry wall are presented. Results from the finite element models are in good agreement with the experimental data