Longitudinal Stiffeners Research Articles

Local buckling behaviour of longitudinally stiffened stainless steel plate girders under combined bending and shear

This paper presents a comprehensive experimental and numerical investigation into the local buckling behaviour of longitudinally stiffened stainless steel plate girders under combined bending moment and shear force. Five plate girders configurated with longitudinal stiffeners with different geometrical proportions and vertical positions were fabricated from austenitic and duplex stainless steel plates. Initial geometric imperfections and material properties were measured, and all plate girders were tested to failure under a three-point loading configuration. The critical buckling strengths, ultimate capacities and failure modes were carefully analysed. Elaborate finite element (FE) models were developed and validated against the test results, and were then used to conduct parametric studies to generate further structural performance data over a wide range of cross-sectional properties, including various geometrical proportions and positions of longitudinal stiffeners, and loading combinations. The obtained test and FE results were utilised to assess the applicability of existing M–V interaction design methods in EN 1993-1-5 and that proposed by Jáger et al. for longitudinally stiffened plate girders. It was indicated that these two M–V interaction curves coupled with the design provisions in EN 1993-1-4 for determining the bending and shear endpoints, offer safe-sided predictions with a good level of consistency and accuracy, for longitudinally stiffened stainless steel plate girders under combined bending and shear. The reliability of these design approaches was further confirmed by statistical analysis.

Behaviour and confinement-based direct design of concrete-filled cold-formed stiffened steel tubular short columns

The advantages of concrete-filled square steel tubular columns are currently being widely utilised in various applications, especially in marine and ocean structures. However, the use of slender cross-sectional tubes significantly reduces the concrete core confining effect due to the local buckling (LB) phenomenon of these tubes. Accordingly, welded stiffeners have been proposed to generate stiffened steel tubes to reduce the effect of LB. But due to welding, residual stress causes significant initial imperfections in the columns. This has resulted in the emergence of the concrete-filled cold-formed stiffened steel tubular (CFSST) columns that consist of cold-formed longitudinal stiffeners embedded in the concrete core. The literature shows that studies into the response of these columns are relatively limited. Accordingly, finite element (FE) modelling of CFSST columns with cold-formed steel tubes is used herein to increase the data bank of these columns. First, available test results on such columns using carbon steels were used to validate the FE models. Then, parametric studies were generated to suggest an innovative lateral confining pressure. These studies were also used to explore the effect of the depth-to-thickness ratio of the outer steel tube, concrete cylindrical strength and stiffener depth on the resistance and behaviour of the square CFSST columns with cold-formed steel tubes. It was found that increasing the cylindrical concrete strength is the most effective way to increase the ultimate strength of the columns, although it decreases the ductility of the columns. In addition, the strengths of CFSST short columns with cold-formed steel tubes were compared with the Japanese, British, European and Chinese codified strengths, which were found to provide conservative predictions. Finally, a new strength was provided for the CFSST short columns with cold-formed steel tubes based on a proposed linear law formula for the lateral confining pressure caused by the stiffened cold-formed tubes.

Technology for erecting monolithic enclosing structures of buildings made of expanded polystyrene concrete

This work aims to develop effective technology for erecting monolithic enclosing structures of buildings made of expanded polystyrene concrete. As a result of the research carried out, a model of large-panel formwork made of ABS plastic for concreting monolithic walls with an expanded polystyrene concrete mixture was developed, representing rectangular panels of a size of 3000 x 1200 x 40 mm. To ensure the necessary strength and rigidity, the outer side of the formwork is made cellular with a large number of longitudinal and transverse stiffeners placed in increments of 300 mm. We have developed a technology for erecting monolithic enclosing structures of buildings made of expanded polystyrene concrete using a mobile concrete-mixing unit. The following are technical and economic indicators for manufacturing monolithic walls out of expanded polystyrene concrete of a volume of 46 m3 : the cost is 354.784 thousand rubles, and the labor intensity and unit capacity are 163.76 people.*h and 27.36 units.*h, respectively. The results significantly offer the construction industry a solution to reduce the labor intensity of construction and installation while manufacturing cost-effective monolithic enclosing structures for buildings.

Hybrid Swarm Intelligence Optimization Methods for Low-Embodied Energy Steel-Concrete Composite Bridges

Bridge optimization is a significant challenge, given the huge number of possible configurations of the problem. Embodied energy and cost were taken as objective functions for a box-girder steel–concrete optimization problem considering both as single-objective. Embodied energy was chosen as a sustainable criterion to compare the results with cost. The stochastic global search TAMO algorithm, the swarm intelligence cuckoo search (CS), and sine cosine algorithms (SCA) were used to achieve this goal. To allow the SCA and SC techniques to solve the discrete bridge optimization problem, the discretization technique applying the k-means clustering technique was used. As a result, SC was found to produce objective energy function values comparable to TAMO while reducing the computation time by 25.79%. In addition, the cost optimization and embodied energy analysis revealed that each euro saved using metaheuristic methodologies decreased the energy consumption for this optimization problem by 0.584 kW·h. Additionally, by including cells in the upper and lower parts of the webs, the behavior of the section was improved, as were the optimization outcomes for the two optimization objectives. This study concludes that double composite action design on supports makes the continuous longitudinal stiffeners in the bottom flange unnecessary.

Design recommendations on longitudinally stiffened titanium-clad bimetallic steel plate girder

In this study, titanium-clad bimetallic steel (TCBS) was innovatively introduced into the plate girder as a web, which enhanced the durability. The ultimate strength of a longitudinally stiffened TCBS plate girder under patch loading was investigated. There were clear differences in the nonlinear properties of the stress–strain curves of Q235 carbon steel, TA1 titanium, and TCBS. The numerical modeling method was verified via an experiment on a TCBS plate girder. A parametric study was performed on the ultimate strength of a longitudinally stiffened TCBS plate girder. The key parameters selected in this study included the position of the longitudinal stiffener, web aspect ratio, web slenderness, and relative load length. The variations in the ultimate strength and the buckling reduction coefficient were examined. The results indicated that the effects of the key parameters on the ultimate strength were clearly different from those on the buckling reduction coefficient. Additionally, the design equations in EN 1993–1–5 were too conservative to be suitable to predict the ultimate strength of the TCBS plate girders subjected to patch loading. Based on the numerical results, a predictive equation for the buckling reduction coefficient of a longitudinally stiffened TCBS plate girder under patch loading was devised. Compared with design equations in EN 1993–1–5, the proposed equation showed better accuracy.

Dynamic Response Control of Stiffened Plate with Hole in Stiffener: A Novel Concept of Additional Open Branched Stiffeners

Modern day structures have found diverse applications of stiffened plates in civil, mechanical, aerospace, marine and offshore engineering. The stiffeners, mainly in the form of beams in these stiffened plates are often exposed to unfavourable environmental and service loads, inducing localized damage to the stiffeners. Sometimes, holes are deliberately made on the stiffeners for passing service pipes, cables etc. Both of the events cause localised loss of stiffness, finally affecting the global dynamic performances. One of the practised techniques to recover the lost stiffness and to safeguard the damaged site is to introduce enclosed prismatic stiffeners around the hole. However, this often fails to critically readjust the localised stiffness loss. A constructive alternate to alleviate such situation, is to provide open branched configurations of additional stiffeners within the near vicinity of the damage. The present research work deals with the demonstration of the suitability of the above solution through numerical modelling of dynamic behaviour of a rectangular isotropic stiffened plate with a central longitudinal stiffener using finite element software ANSYS. The damage, represented equivalently as a circular cut-out in the stiffener, is considered to be located arbitrarily. Free vibration characteristics viz. natural frequencies and mode shapes of the plate in undamaged and damaged conditions have been determined by solving eigenvalue problem employing Block Lanczos algorithm. Various configurations of open-branched stiffeners around the circular cut-out, placed at specified locations have been explored. The sensitivities of relevant geometric parameters, such as the distance of the branching from the damage site, orientations of the branching etc. indicate that it is possible to design a system of open branched stiffeners around a damaged site of a stiffener to keep the overall dynamic responses practically unchanged. Such idea of branched stiffener is novel and has potential practical applications towards damage mitigation of various engineering infrastructures.

Effect of local cut-out on fatigue strength assessment in ship structures

The aim of the work is to evaluate different design alternatives to obtain criteria for the selection of the most effective design by fatigue strength assessment of the local cut-out as a result of the connection between the longitudinal or ordinary stiffener and the transverse web frame (longi-web) in the side hull structure (upper wing torsional box), very important area due to its high stress concentration, of a container vessel, one of the most important ships in terms of its influence on the world economy. Structural solutions and design guidelines are established, by means of numerical models validated by experimental tests, which allow alternative designs to be obtained that improve their fatigue behaviour. Standard cut-out geometries are studied under the presence of different variables (radius of curvature, longitudinal spacing, longitudinal stiffener cross-section, and flange arrangement) that are evaluated to determine their effect in the structural assessment (fatigue damage, stress concentration, and fracture mechanics) and the weight comparison between alternatives.

Experimental study on buckling behavior of orthotropic steel deck with slender open ribs for large span suspension bridges

This paper presents an experimental and numerical study of the buckling behavior of the orthotropic steel deck with slender open ribs for the Zhangjinggao Yangtze River Bridge. Eight specimens consisting of four longitudinal stiffeners and a top deck plate were fabricated and subjected to axial compression loading tests. Finite element simulations and a parametric discussion were carried out using ANSYS software. Experimental results demonstrated that the axial buckling failure mode was characterized by stiffener tripping before the yielding of ribs. The post-buckling stage showed a certain ductility when the ribs did not collapse simultaneously. A buckling strength of 323 MPa was obtained from the tests, which reflected a sufficient safety margin compared to the working stresses in the real bridge. The numerical results agreed reasonably well with the tests. The study showed that the ratio of buckling stress to yield strength ranged from 0.72 to 0.84. Besides, geometric imperfections, residual stresses, and vehicle loads merely degrade the buckling strength to a small extent according to the parametric discussion.

Flexural behaviour and design rules for SupaCee sections with web openings

Cold-Formed Steel (CFS) has been used to a great extent due to the industry uptake given its merits with the key being its high strength-to-weight ratio. Besides, innovative section profiles are constantly introduced to uplift the structural applicability of CFS sections. SupaCee section is a novel section with enhanced structural performance due to its sectional attributes such as longitudinal web stiffeners and return lips. However, the necessity of web openings (holes) to provide service integrations is not considered adequately so far in previous studies with SupaCee sections. Hence, this study reports a comprehensive assessment on flexural performance of SupaCee sections with web openings. Accordingly, numerical analysis was carried out which followed by the validation of the elaborated Finite Element (FE) model and the development of parametric studies considering key parameters such as depth, thickness, yield strength, web opening ratio and hole spacing. Results from the numerical studies are discussed and compared with existing design standards. New design provisions are proposed to predict the flexural capacity of SupaCee sections with web openings. Moreover, FE model of Lipped Channel Beam (LCB) was developed and analysed with similar parameters of SupaCee sections. The comparison of LCB and SupaCee sections with and without web openings are reported and based on the flexural capacity comparisons; recommendations are stated to replace conventional CFS sections by SupaCee sections.

Optimal design of steel–concrete composite bridge based on a transfer function discrete swarm intelligence algorithm

Bridge optimization can be complex because of the large number of variables involved in the problem. In this paper, two box-girder steel–concrete composite bridge single objective optimizations have been carried out considering cost and CO_{2} emissions as objective functions. Taking CO_{2} emissions as an objective function allows to add sustainable criteria to compare the results with cost. SAMO2, SCA, and Jaya metaheuristics have been applied to reach this goal. Transfer functions have been implemented to fit SCA and Jaya to the discontinuous nature of the bridge optimization problem. Furthermore, a Design of Experiments has been carried out to tune the algorithm to set its parameters. Consequently, it has been observed that SCA shows similar values for objective cost function as SAMO2 but improves computational time by 18% while also getting lower values for the objective function result deviation. From a cost and CO_{2} optimization analysis, it has been observed that a reduction of 2.51 kg CO_{2} is obtained by each euro reduced using metaheuristic techniques. Moreover, for both optimization objectives, it is observed that adding cells to bridge cross-sections improves not only the section behavior but also the optimization results. Finally, it is observed that the proposed design of double composite action in the supports allows to remove continuous longitudinal stiffeners in the bottom flange in this study.

Assessment on seismic performance of circular concrete-filled thin-walled steel tube columns

Concrete-filled steel tubular (CFST) with circular section is a very efficient composite component bearing vertical loads, which takes advantage of the synergy of steel tube and concrete to fully develop the strengths of both materials. To promote the application of circular CFST columns in multi-story buildings or medium-span bridge piers with improved economic efficiency, circular CFSTs using thin-walled steel tubes were studied in this paper. 8 specimens were designed and tested to assess their seismic performance under constant axial compression and cyclic lateral loads. The key test parameters include axial compression ratio, diameter-to-thickness ratio of steel tube, as well as stiffening scheme. The effectiveness of two steel plate stiffeners (longitudinal stiffener, binding stiffener) at the potential plastic hinges of thin-walled circular CFST columns was verified and discussed. Although all specimens failed in a manner characterized by significant local buckling of steel tubes, they still performed a relatively ductile behavior with the ductility coefficients generally exceeding 4.0, and the ultimate drift ratios exceeding 1/40. The steel plate stiffeners did not achieve the expected enhancement in strength and ductility, due to the premature fracture in the steel tube which may be caused by the damage in the welding heat-affected zone. Based on the test results, a numerical model and a simplified hysteretic model were established to predict the seismic responses of the thin-walled circular CFST columns.

Influence of Longitudinal Stiffeners on the Local Stresses in Crane Runway Girders ‐ Experimental and Numerical Investigations

AbstractCrane runway girders with slender webs are often strengthened by additional longitudinal stiffeners to avoid local plate buckling of the web. It is expected that this leads to an increase of local vertical bending stresses near the top edge of the web due to eccentric wheel loads. These local stresses have a significant impact on the fatigue design of the flange‐to‐web connections and the required girder dimensions. However, the current design model in EN 1993‐6 for crane supporting structures does not consider this effect. In order to study this behaviour in detail, laboratory tests and numerical finite element calculations are carried out on crane runway girders with longitudinal stiffeners at different positions of the web. It is verified that the local stresses increase with decreasing distance of the stiffeners from the top edge of the web plate. Based on these results and a modified proposal from literature, the design model in EN 1993‐6 is extended to also cover additional stiffeners. Finally, the model is validated through a comparison with tests and numerical calculations.

Patch Loading Resistance of Slender Plate Girders with Multiple Longitudinal Stiffeners

AbstractThere is currently no reliable and simple design method available in international literature for the determination of the patch loading resistance of slender plate girders having multiple longitudinal stiffeners. Previous investigations focused mainly on girders having one longitudinal stiffener, which is not the common case for box‐girder bridges. Therefore, the current research – partly published in this paper – has a focus on the patch loading resistance of slender web girders having multiple longitudinal stiffeners. An advanced numerical model is developed and verified by own laboratory test results to determine the patch loading resistance. A numerical parametric study is executed to investigate the load‐carrying capacity of girders having typical bridge geometries. Analysing the numerical simulation results the structural behavior obtained is classified based on the stiffener stiffness. Effect of the different geometrical parameters on the patch loading resistance is evaluated with special focus on the stiffener stiffness and distance between the longitudinal stiffeners. The failure modes depending on the stiffener stiffness are investigated and the local buckling type failure is characterised by a minimum stiffness. For this specific failure mode an improved design method is developed for girders having multiple longitudinal stiffeners giving reliable resistance for the analysed cases within the analysed parameter range. The presented resistance model is consistent with the design philosophy of EN1993‐1‐5.

Shape Optimisation of Cold‐Formed Steel Cross‐Sections with Longitudinal Intermediate Stiffeners

AbstractThis paper reports the development, numerical implementation and application of a novel methodology to perform a multi‐objective shape optimisation of conventional cold‐formed steel (CFS) cross‐section shapes with longitudinal intermediate stiffeners, manufactured by bending the steel sheets with roll‐forming machines. The methodology is based on a Genetic Algorithm (GA) and aims at maximising the compressive and/or flexural ultimate strength of CFS members currently used in industry with respect to local, distortional and local‐distortional interactive failures. The design approach adopted to estimate the member ultimate strengths is based on the Direct Strength Method (DSM) and Generalised Beam Theory (GBT) is used to calculate the elastic buckling loads and moments. The proposed methodology consists of adding small intermediate stiffeners, whose possible locations are pre‐defined in accordance with a map of executable fold‐line positions – the original cross‐section typology, overall dimensions and wall angles are retained. The application and potential of the developed GA‐based code is illustrated by addressing the optimisation of conventional lipped channel, lipped zed and rack cross‐section shapes for CFS members subjected to compression, bending or compression and bending.

Dimensioning Aids for Stiffened and Unstiffened Plates According to Eurocode 3 Part 1‐5

AbstractIn Germany stiffened plate in bridge construction must be verified using the method of reduced stresses (MRS) according to DIN EN 1993‐1‐5 [2, 3]. Unstiffened plates on the other hand may be verified either according to the effective widths method or according to the reduced stress method. In order to shorten the time‐consuming verification of the standardised verification formats for pre‐dimensioning which is particularly prevalent for stiffened plates diagrams are developed and presented in the present paper on the basis of the MRS by reformulating the buckling verification which enable a quick pre‐dimensioning. With the diagrams, the dimensioning of plate thicknesses and stiffener spacings can be carried out in a few simple and comprehensible steps. The diagrams are selected on the basis of the geometry parameters .a, b. and t or the applicable boundary conditions. For stiffened plate, the maximum permissible spacing of the longitudinal stiffeners or the required main plate thickness can be determined. Diagrams for the dimensioning of longitudinal stiffeners by determining minimum stiffnesses are also presented. The minimum stiffnesses are derived from the geometry of the linear buckling shapes of simply stiffened plate.

Experimental and numerical studies on mechanical behavior of stiffened concrete‐filled square steel tube columns subjected to axial compression

AbstractIn this study, nine square concrete‐filled steel tubular (SCFST) columns considering longitudinal stiffeners as parameters were produced to investigate the axial compression mechanical properties of SCFST columns in the condition of constant steel consumption. This included one specimen without stiffeners, three specimens stiffened with one stiffener on each tube wall, two specimens stiffened with two stiffeners on each tube wall, two specimens stiffened with three stiffeners on each tube wall and one specimen stiffened with four stiffeners on each tube wall. Simultaneously, numerical simulations were performed under identical conditions using ABAQUS software. The results showed that the longitudinal stiffeners can act as an out‐of‐plane restriction support to delay the development of local buckling of the steel tube, which indirectly improved the constraint effect of steel tube on core concrete. First, both the number of local buckling and the ultimate displacement of the specimens grew correspondingly when the number of stiffeners increased. As the sub‐wall width‐to‐thickness ratio was increased, the steel tube became prone to local buckling. Second, the installation of stiffeners decreased the confinement effect of steel tube on the core concrete, in which the sub‐wall width‐to‐thickness ratio and the stiffener width‐to‐thickness ratio had a great influence on the ultimate bearing capacity of the specimens. Further, the experimental outcomes indicated that the bearing capacity of stiffened specimens was less than that of the unstiffened specimen. The bearing capacity of the specimens stiffened with three and four stiffeners was higher than that of the specimens stiffened with one and two stiffeners. Third, the stiffener width‐to‐thickness ratio had a considerable impact on the ductility of the specimens. The ductility of specimens stiffened with one and two stiffeners was greater than that of the specimens stiffened with three and four stiffeners. Finally, the finite element simulations were consistent with the experimental process. The confinement factor of stiffened specimens became enlarged when either the number of stiffeners in the same thickness condition increased or the thickness of steel tube wall under condition of the same number of stiffeners grew.

Effect of the Torsion Box Dimensions on Local Stress Distribution and Fatigue Strength Assessment of a Container Ship

The aim of this paper is to estimate the influence of the dimensions of the torsion box (height and width), of a 2400 TEU feeder-class container ship, on local stress distribution and assessment of local fatigue strength by using a numerical approach based on the fatigue limit-state and ultimate limit-state in the midship region. In terms of the fatigue limit-state, the effect of the dimensions of the torsion box is obtained by geometrical modifications, in the connection between the side shell longitudinal stiffeners with the transverse web frame for nine structural details, referring to different arrangements of strengthening elements (brackets and flat bars). The process of comparing the different elements determines the most effective combination. This structural influence on the local stress distribution is assessed, along the longitudinal plates between ordinary stiffeners bounding the perimeter of the torsion box, by calculating the hull girder stresses, local buckling stresses and shear stress distribution induced by vertical and horizontal shear forces, Saint Venant and warping torques, and finally the shear stresses induced by a warping moment. Scantling criteria are obtained allowing for a better design of this very important region in container ships.

Behaviour of cold-formed steel-concrete composite columns under axial compression: Experimental and numerical study

Concrete filled cold-formed steel-concrete composite columns exhibit improved strength and ductility characteristics due to its ability to resist inward buckling as well as delay the outward buckling. Though concrete infill prevents inward buckling, outward buckling still limits the steel section from reaching its yield strength. From the past studies, it is observed that the introducing of web stiffeners in cross-section of steel section may improve its buckling resistance. The present study focuses on assessing the effect of longitudinal stiffeners on the behaviour of square cold-formed steel–concrete composite columns for the various slenderness range (0.01 to 0.4) through experimental and numerical studies. Conventionally, the integrity of hollow tube cross sections is ensured by welding or by rolling process during the manufacturing. Welding process cannot be adopted in thin-walled cold formed sections since it may lead to higher degree of imperfection. In this study, the desired square cross sections were formed from flat steel sheet and overlapped using self-tapping screws. An intensive numerical analysis was carried out by varying stiffener angle as 90°, 120°, and 141° and the buckling curves for plain and profiled sections were presented. It is concluded that the axial compressive strength of plain and stiffened composite sections is almost equal, attributed to the inability of concrete to reach its maximum stress due to stress concentration at the stiffeners’ edges. The buckling reduction factor of stiffened composite columns showed higher values in the higher slenderness range, indicating the positive effect of the stiffeners.

Stiffening optimisation of conventional cold-formed steel cross-sections based on a multi-objective Genetic Algorithm and using Generalised Beam Theory

This paper reports the development, numerical implementation and application of a novel methodology to perform a multi-objective stiffening optimisation of conventional cold-formed steel (CFS) cross-section shapes with longitudinal intermediate stiffeners, manufactured by bending the steel sheets with roll-forming machines. The methodology is based on a Genetic Algorithm (GA) and aims at maximising the compressive and/or flexural ultimate strength of CFS members currently used in industry with respect to local, distortional and local-distortional interactive failures. The design approach adopted to estimate the member ultimate strengths is based on the Direct Strength Method (DSM) and Generalised Beam Theory (GBT) is used to calculate the elastic buckling loads and moments. The proposed methodology consists of adding small intermediate stiffeners, whose possible locations are pre-defined in accordance with a map of executable fold-line positions, thus leading to an optimisation procedure whose output are alternative (stiffened) cross-sections that (i) outperform the original conventional/plain cross-section and (ii) can be fabricated with a minimal additional cost – the original cross-section typology, overall dimensions and wall angles are retained. The application and potential of the developed GA-based code is illustrated by addressing the stiffening optimisation of conventional lipped channel, lipped zed and rack cross-section shapes for CFS members subjected to compression, bending or compression and bending – the numerical results are presented in terms of cross-section families belonging to the optimal Pareto Front. For validation and assessment purposes, some optimised cross-sections obtained are compared with the “exact” solutions provided by a “brute-force search”.

Experimental study on smoke flow behaviour under ships’ deck structures in early stages of fire

In ships’ cargo spaces carrying vehicles, so called “vehicle spaces”, fire has sometimes taken place and safety measures against such fire is under discussion at the International Maritime Organization (IMO). Early detection of fire is one of the essential elements of such safety measures. Location of fire detectors affects swiftness of detection of fire, and in onshore buildings, fire detectors are generally installed directly on ceilings because there are no obstacles under ceilings and smoke spreads along the ceilings. On the other hand, structures below ceilings, i.e., decks, of vehicle spaces are quite different from those of onshore buildings due to strength members below a deck, such as stiffeners and web beams. The appropriate positions of smoke detectors in a vehicle space, including vertical positions of detectors from a ceiling, has not been well-understood, while the maximum coverage of a detector is determined by an international regulation. In this study, the effect of structures below the ceilings of vehicle spaces on detection of fire has been investigated and the appropriate positions of smoke detectors including vertical positions have been considered, in particular, for smouldering fire sources. For this purpose, a one-sixth scaled deck model was prepared to simulate a part of a vehicle space and fire experiments were conducted using a small-scaled fire source. The effect of the structure on a smoke flow beneath the ceiling was experimentally investigated under the condition that the flow had a weak driving force in a smouldering fire or an early stage of fire. In the experiment, the flow was visualized using a laser and the smoke density expressed with the extinction coefficient was also measured. In addition, a small flaming fire source was used during the experiment, to further investigate a possibility of detection in an early stage of fire. The vertical profiles of smoke density were measured using the laser transmissometer. Furthermore, a smoke flow was visualized using continuous wave laser. As the results, it is concluded that it is appropriate to install smoke detectors at the lower end of the longitudinal stiffener, instead of installing on the ceilings in vehicle spaces.