Effects of weld size on stress concentration factors of CHS-CFSHS joints

This paper aims to disclose the effects of weld size on hot spot stress in the calculation of fatigue performance of the joints. For this purpose, the author explored the hot spot stress of CHS-CFSHS T-joints, which consists of circular hollow section (CHS) braces and concrete-filled square hollow section (CFSHS) chords. After reviewing the previous studies and the relevant specifications on weld size, the author probes into the effects of weld size on the stress concentration factor (SCF) of CHS-CFSHS joints via finite-element analysis. The analysis show that the weld size directly affected the hot spot stress in both conditions, and the influence laws were largely the same; with the increase of weld size, the brace-side SCF plunged when the chord-size weld size remained the same, but the chord-side SCF changed slightly when the brace-side weld size was constant; the brace-side and chord-side SCF declined when the brace-side and chord-side weld sizes increased by the same amount. This research successfully determined the weld sizes that are consistent with the relevant specifications, and safe and simple to apply in actual engineering

Effects of weld size on stress concentration factors of CHS-CFSHS joints

This paper aims to disclose the effects of weld size on hot spot stress in the calculation of fatigue performance of the joints. For this purpose, the author explored the hot spot stress of CHS-CFSHS T-joints, which consists of circular hollow section (CHS) braces and concrete-filled square hollow section (CFSHS) chords. After reviewing the previous studies and the relevant specifications on weld size, the author probes into the effects of weld size on the stress concentration factor (SCF) of CHS-CFSHS joints via finite-element analysis. The analysis show that the weld size directly affected the hot spot stress in both conditions, and the influence laws were largely the same; with the increase of weld size, the brace-side SCF plunged when the chord-size weld size remained the same, but the chord-side SCF changed slightly when the brace-side weld size was constant; the brace-side and chord-side SCF declined when the brace-side and chord-side weld sizes increased by the same amount. This research successfully determined the weld sizes that are consistent with the relevant specifications, and safe and simple to apply in actual engineering

PerceptionGPT: Effectively Fusing Visual Perception into LLM

The integration of visual inputs with large language models (LLMs) has led to remarkable advancements in multi-modal capabilities, giving rise to visual large language models (VLLMs). However, effectively harnessing VLLMs for intricate visual perception tasks remains a challenge. In this paper, we present a novel end-to-end framework named PerceptionGPT, which efficiently and effectively equips the VLLMs with visual perception abilities by leveraging the representation power of LLMs' token embedding. Our proposed method treats the token embedding of the LLM as the carrier of spatial information, then leverage lightweight visual task encoders and decoders to perform visual perception tasks (e.g., detection, segmentation). Our approach significantly alleviates the training difficulty suffered by previous approaches that formulate the visual outputs as discrete tokens, and enables achieving superior performance with fewer trainable parameters, less training data and shorted training time. Moreover, as only one token embedding is required to decode the visual outputs, the resulting sequence length during inference is significantly reduced. Consequently, our approach enables accurate and flexible representations, seamless integration of visual perception tasks, and efficient handling of a multiple of visual outputs. We validate the effectiveness and efficiency of our approach through extensive experiments. The results demonstrate significant improvements over previous methods with much fewer trainable parameters and GPU hours, which facilitates future research in enabling LLMs with visual perception abilities

Turbulent wind field simulation of wind turbine structures with consideration of the effect of rotating blades

In order to achieve the wind-induced vibration response analysis and fatigue analysis, this study conducts the wind field simulations around tubular tower and rotating blades of typical pitch-controlled 1.25MW wind turbine structures, respectively. Based on field test data, there is a large difference between the turbulent wind spectrum for the rotating blades and classic wind spectrum adopted by the non-rotating blades and tubular tower. In this study, first, the auto and crossrotational Fourier spectrums are deduced based on the physical mechanism, with particular focus on the influences of the rotational effect and the correlation between different points located on the same and different blades. Then, the Davenport type coherence function is optimized. The high accuracy of the rotational Fourier spectrum model is verified by comparing with the real data. Relevant parameter analysis of the rotational Fourier spectrum is conducted. Finally, turbulent wind fields around the tubular tower based on the Kaimal spectrum and the rotating blades based on the rotational Fourier spectrum are simulated by means of the harmony superposition method. The results indicate that the calculated wind spectrums have good agreement with the target wind spectrums. Therefore, the proposed approach in this study is feasible for the turbulent wind field simulation of wind turbine structures

Modified stress intensity factor equations for semi-elliptical surface cracks in finite thickness and width plates

Weld defects and severe variation of shape near the welds cause high stress concentration at weld toes or weld roots. This high stress concentration reduces fatigue lives of welded structures. A stress intensity factor (SIF) which includes this effect increases the accuracy of fatigue lives prediction. A magnification factor is commonly used to multiply the SIF of semi-elliptical surface cracks to account for the stress concentration effect in welded connections. Yamada and Hirt model is one of these methods. Comparison between Yamada & Hirt SIF equations and Newman & Raju SIF equations are applied to SIF of semi-elliptical surface cracks. The results suggest that Yamada & Hirt SIF equations are valid when the crack aspect ratio is less than 0.6. New empirical SIF equations are developed based on Yamada & Hirt SIF equations. The newly derived SIF equations are verified by comparing with experimental data

Fatigue tests and design of welded thin-walled RHS-Channel and Channel-Channel cross-beam connections under cyclic bending

Research on fatigue strength of welded galvanized cross-beam connections has been carried out and reported. Previous research focused on cross-beams made up of rectangular hollow sections (RHS) and Angle sections; RHS-RHS as well as RHS-Angle cross-beam connections and was published in Thin-Walled Structures, 48 (2010) 159-168. This paper reports on the fatigue strength of cross-beam connections made up of rectangular hollow sections (RHS) and Channel sections; RHS-Channel and Channel-Channel cross-beam connections. Fatigue tests on RHS-Channel and Channel-Channel cross-beam connections were carried out under cyclic bending in the bottom member. The resultant failure modes during the fatigue tests are reported. The crack growth patterns that are observed leading to failure are studied in relation to the stress concentration factors (SCFs) from sample specimens. The stress concentration factors (SCFs) are determined from stress measurements around the hot spots of the sample specimens. The resultant RHS-Channel and Channel-Channel S-N data is compared to S-N data of cross-beam connections from previous research. A comparison of the S-N data with existing fatigue design curves in the Australian Standard, AS4600, gives an indication of the class that can be adopted for the fatigue design of RHS-Channel and Channel-Channel cross-beam connections under cyclic bending using deterministic methods. Statistical analyses of the S-N data are also carried out to determine recommended design curves for the RHS-Channel and Channel-Channel cross-beam connections for both the classification and hot spot stress method

Fatigue tests and design of thin CHS–SHS T-joints under cyclic in-plane bending

Agricultural equipments, such as linkage graders, haymakers, swing-ploughs, bale handlers and road transport equipments, such as road trailers, traffic sign supports and lighting poles are manufactured using welded thin-walled (t<4 mm) hollow section connections. There are currently no fatigue design rules for nodal joints made up of thicknesses less than 4 mm in existing fatigue design standards such as CIDECT Design Guide No.8. Previous research on welded thin-walled joints covered plate-to-SHS (square hollow section) and SHS-to-SHS T-joints. This paper describes fatigue tests on T-joints made up of thin-walled (t<4 mm) SHS chords and circular hollow section (CHS) braces, namely CHS–SHS T-joints. The joints were tested under constant stress amplitude cyclic in-plane bending in the brace. In all the 18 CHS–SHS T-joints tested, chord-tension-side failure mode was observed. Using the experimental stress concentration factors (SCFs) obtained through stress distribution measurement at weld toes in the chord and SCFs from existing parametric equations, fatigue design recommendations are proposed

Experimental investigation on static flexural behavior of fatigue damaged SRC beams strengthened with CFRP sheets

This paper presents an experimental investigation on CFRP strengthening of severely fatigue damaged SRC (steel-reinforced concrete) beams. Bending tests were carried out on three types of SRC beams: (1) SRC beams without any damage, (2) damaged SRC beams repaired by welding and (3) damaged SRC beams repaired by welding and CFRP. Failure modes of different types of SRC beams were compared. The effects of fatigue loading history and CFRP on static performance of SRC beams were studied. The experimental results showed that, for the fatigue damaged SRC beams, flexural bearing capacity can be restored if they were repaired by welding fractured beams and re-bars even without CFRP sheets, but the plastic strengthening of encased steel is weakened. CFRP sheets can effectively increase the ultimate flexural bearing capacity and overall stiffness of SRC beams. Meanwhile, it can delay crack propagation, reduce the width of surface cracks, and decrease the deflection under yield load and ultimate load. Finally, the strength of CFRP sheets will be fully utilized by using end anchorages

Finite element modelling for SCFs in steel tubular T-joints with concrete-filled chords under axial loading in the brace

Stress concentration factor (SCF) analysis is carried out for welded T-joints made up of steel circular hollow section brace welded onto concrete-filled circular hollow section chord. A finite element model has been developed employing ABAQUS software to simulate the performance of T-joints with concrete-filled chords under axial force on the brace. Modelling of the weld profile has been included in the simulation. An 8-node 3D hexahedral solid element with full integration scheme has been employed in the simulation. The interaction between the chord and concrete filling has been assumed to be due to friction only. The hot spot stresses have been obtained by linear extrapolation of the stresses in the region recommended by CIDECT. The outcome of the numerical simulation is verified using existing experimental results obtained by Wang et al. (2013)

Fatigue behavior and design of welded tubular T-joints with CHS brace and concrete-filled chord

Concrete-filled welded tubular structures have been increasingly used in large-span constructions such as truss bridges where fatigue failure is always a critical issue that should be focused on. This paper deals with fatigue behavior of CHS-CFSHS T-joints, which are made up of circular hollow section (CHS) braces and concrete-filled square hollow section (CFSHS) chords. Experimental results on stress concentration factor (SCF) were briefly summarized. Fatigue tests were conducted under cyclic tensile force in the brace, so that cracking patterns, failure modes and fatigue data of such joints were recorded. The tested CHS-CFSHS T-joints suffered from one of the following three failure modes: (i) brace-90°-side failure, (ii) chord-90°-side failure, (iii) chord-0°-side failure. Based on the fatigue data in terms of hot spot stress range (Sr,hs) versus number of cycles (N), fatigue design Sr,hs-N curves were determined using the deterministic and least-squares methods, respectively. It was found that most of the existing Sr,hs-N curves are unsafe for fatigue design of CHS-CFSHS T-joints, except for the X´ Sr,hs-N curve recommended by American Petroleum Institute [32] and American Welding Society [36]. In addition, the fatigue data of the CHS-CFSHS T-joints were found comparable with CHS-CFCHS T-joints (T-joints with CHS brace and concrete-filled CHS chord), hence a new fatigue design Sr,hs-N curve was proposed for the both types of concrete-filled joints. A comparison between CHS-CFSHS T-joints and empty CHS-SHS T-joints showed that CHS-CFSHS T-joints generally have better fatigue behavior compared to their empty counterparts except for the case of extremely large ratio of brace diameter to chord width (β)