3,273 research outputs found
Improving construction materials management practices in construction sites
Construction Materials Management is a vital function for improving productivity in construction projects. Poor materials management can often affect the overall construction time, quality and budget. Currently, the construction material management practice in Somalia is believed to be poorly performed. Lack of standardized construction materials management system is one of the key issues facing by the building industry in Mogadishu-Somalia. The aim of this study was to investigate the current practices of material management at construction sites in Mogadishu-Somalia. A questionnaire survey study design was used to explore construction materials management practices. Fifty questionnaires were distributed to project managers, project engineers, site engineers, engineer, and foreman, and they were received and analysed. The following data analysis techniques were used: descriptive statistics were conducted to report sample characteristics, reliability and validity analyses were performed to confirm robustness of the instrument, graphical presentation such as bar charts were developed, and finally Average Mean Index Scale were constructed. The study results reveals that, 46.7% of respondent’s organization obtain materials for sites without site requisition by site engineer provisions, while 28.9% of respondent’s organization procure materials for sites with site requisition by project manager provisions and 13.3% of respondent’s organization procure materials for site by engineer. The results indicated that currently there is no standardized and computerized construction materials management system applied in Somalia. The researcher concluded that all contracting companies are interested in using some techniques of managing construction materials such as creating and updating database for materials categories from local and international suppliers. Finally, researcher recommends to use computerized construction materials management systems to reduce effort and time, and to achieve more accurate results
A Joint 3D-2D based Method for Free Space Detection on Roads
In this paper, we address the problem of road segmentation and free space
detection in the context of autonomous driving. Traditional methods either use
3-dimensional (3D) cues such as point clouds obtained from LIDAR, RADAR or
stereo cameras or 2-dimensional (2D) cues such as lane markings, road
boundaries and object detection. Typical 3D point clouds do not have enough
resolution to detect fine differences in heights such as between road and
pavement. Image based 2D cues fail when encountering uneven road textures such
as due to shadows, potholes, lane markings or road restoration. We propose a
novel free road space detection technique combining both 2D and 3D cues. In
particular, we use CNN based road segmentation from 2D images and plane/box
fitting on sparse depth data obtained from SLAM as priors to formulate an
energy minimization using conditional random field (CRF), for road pixels
classification. While the CNN learns the road texture and is unaffected by
depth boundaries, the 3D information helps in overcoming texture based
classification failures. Finally, we use the obtained road segmentation with
the 3D depth data from monocular SLAM to detect the free space for the
navigation purposes. Our experiments on KITTI odometry dataset, Camvid dataset,
as well as videos captured by us, validate the superiority of the proposed
approach over the state of the art.Comment: Accepted for publication at IEEE WACV 201
A Study on Recent Developments and Issues with Obstacle Detection Systems for Automated Vehicles
This paper reviews current developments and discusses some critical issues with obstacle detection systems for automated vehicles. The concept of autonomous driving is the driver towards future mobility. Obstacle detection systems play a crucial role in implementing and deploying autonomous driving on our roads and city streets. The current review looks at technology and existing systems for obstacle detection. Specifically, we look at the performance of LIDAR, RADAR, vision cameras, ultrasonic sensors, and IR and review their capabilities and behaviour in a number of different situations: during daytime, at night, in extreme weather conditions, in urban areas, in the presence of smooths surfaces, in situations where emergency service vehicles need to be detected and recognised, and in situations where potholes need to be observed and measured. It is suggested that combining different technologies for obstacle detection gives a more accurate representation of the driving environment. In particular, when looking at technological solutions for obstacle detection in extreme weather conditions (rain, snow, fog), and in some specific situations in urban areas (shadows, reflections, potholes, insufficient illumination), although already quite advanced, the current developments appear to be not sophisticated enough to guarantee 100% precision and accuracy, hence further valiant effort is needed
Development of bent-up triangular tab shear transfer (BTTST) enhancement in cold-formed steel (CFS)-concrete composite beams
Cold-formed steel (CFS) sections, have been recognised as an important
contributor to environmentally responsible and sustainable structures in developed
countries, and CFS framing is considered as a sustainable 'green' construction material
for low rise residential and commercial buildings. However, there is still lacking of data
and information on the behaviour and performance of CFS beam in composite
construction. The use of CFS has been limited to structural roof trusses and a host of nonstructural applications. One of the limiting features of CFS is the thinness of its section
(usually between 1.2 and 3.2 mm thick) that makes it susceptible to torsional,
distortional, lateral-torsional, lateral-distortional and local buckling. Hence, a reasonable
solution is resorting to a composite construction of structural CFS section and reinforced
concrete deck slab, which minimises the distance from the neutral-axis to the top of the
deck and reduces the compressive bending stress in the CFS sections. Also, by arranging
two CFS channel sections back-to-back restores symmetricity and suppresses lateraltorsional and to a lesser extent, lateral-distortional buckling. The two-fold advantages
promised by the system, promote the use of CFS sections in a wider range of structural
applications. An efficient and innovative floor system of built-up CFS sections acting
compositely with a concrete deck slab was developed to provide an alternative composite
system for floors and roofs in buildings. The system, called Precast Cold-Formed SteelConcrete Composite System, is designed to rely on composite actions between the CFS
sections and a reinforced concrete deck where shear forces between them are effectively
transmitted via another innovative shear transfer enhancement mechanism called a bentup triangular tab shear transfer (BTTST). The study mainly comprises two major
components, i.e. experimental and theoretical work. Experimental work involved smallscale and large-scale testing of laboratory tests. Sixty eight push-out test specimens and
fifteen large-scale CFS-concrete composite beams specimens were tested in this program.
In the small-scale test, a push-out test was carried out to determine the strength and
behaviour of the shear transfer enhancement between the CFS and concrete. Four major
parameters were studied, which include compressive strength of concrete, CFS strength,
dimensions (size and angle) of BTTST and CFS thickness. The results from push-out test
were used to develop an expression in order to predict the shear capacity of innovative
shear transfer enhancement mechanism, BTTST in CFS-concrete composite beams. The
value of shear capacity was used to calculate the theoretical moment capacity of CFSconcrete composite beams. The theoretical moment capacities were used to validate the
large-scale test results. The large-scale test specimens were tested by using four-point
load bending test. The results in push-out tests show that specimens employed with
BTTST achieved higher shear capacities compared to those that rely only on a natural
bond between cold-formed steel and concrete and specimens with Lakkavalli and Liu
bent-up tab (LYLB). Load capacities for push-out test specimens with BTTST are
ii
relatively higher as compared to the equivalent control specimen, i.e. by 91% to 135%.
When compared to LYLB specimens the increment is 12% to 16%. In addition, shear
capacities of BTTST also increase with the increase in dimensions (size and angle) of
BTTST, thickness of CFS and concrete compressive strength. An equation was
developed to determine the shear capacity of BTTST and the value is in good agreement
with the observed test values. The average absolute difference between the test values
and predicted values was found to be 8.07%. The average arithmetic mean of the
test/predicted ratio (n) of this equation is 0.9954. The standard deviation (a) and the
coefficient of variation (CV) for the proposed equation were 0.09682 and 9.7%,
respectively. The proposed equation is recommended for the design of BTTST in CFSconcrete composite beams. In large-scale testing, specimens employed with BTTST
increased the strength capacities and reduced the deflection of the specimens. The
moment capacities, MU ) e X p for all specimens are above Mu>theory and show good agreement
with the calculated ratio (>1.00). It is also found that, strength capacities of CFS-concrete
composite beams also increase with the increase in dimensions (size and angle) of
BTTST, thickness of CFS and concrete compressive strength and a CFS-concrete
composite beam are practically designed with partial shear connection for equal moment
capacity by reducing number of BTTST. It is concluded that the proposed BTTST shear
transfer enhancement in CFS-concrete composite beams has sufficient strength and is
also feasible. Finally, a standard table of characteristic resistance, P t a b of BTTST in
normal weight concrete, was also developed to simplify the design calculation of CFSconcrete composite beams
Review of Machine Vision-Based Electronic Travel Aids
Visual impaired people have navigation and mobility problems on the road. Up to now, many approaches have been conducted to help them navigate around using different sensing techniques. This paper reviews several machine vision- based Electronic Travel Aids (ETAs) and compares them with those using other sensing techniques. The functionalities of machine vision-based ETAs are classified from low-level image processing such as detecting the road regions and obstacles to high-level functionalities such as recognizing the digital tags and texts. In addition, the characteristics of the ETA systems for blind people are particularly discussed
- …