Construction Load Research Articles

Seismic performance of high-capacity light wood frame shear walls with three rows of nails

With the increase of building height for light wood-frame construction and seismic loads in National Building Code of Canada 2015, stronger shear wall systems have been facing higher demands, especially for mid-rise wood-frame buildings located in high seismic zones. In collaboration with FPInnovations, a new high-capacity shear wall system with two or three rows of nails was developed. This paper presents the test results of shear walls with three rows of nails. A total of 12 specimens (with two standard shear wall specimens as a reference) were tested under reversed cyclic loading. Test results show that shear walls with three rows of nails have approximately-three times the lateral load resistance of a standard shear wall with the same sheathing thickness, nail diameter and nail spacing. The initial stiffness and ultimate displacement of the high-capacity shear wall are also greater than the comparable standard shear wall. Seismic equivalency to standard shear walls in accordance with ASTM D7989 was also conducted. Although shear walls with three rows of nails have three times of lateral load capacities of a standard shear wall, their design values are less than twice the design values of the standard shear walls. This is mainly due to the fact that a higher over-strength factor has to be used to meet the ductility criteria in ASTM D7989.

Stability analysis of foundation pit against uplift based on circular sliding

The analytical solution of the basal stability coefficient for the excavation is obtained, basing on the principle of mechanical balance and the theory of calculus. The programmatic calculation of the analytical solution is realized with the VB6.0 platform. Furthermore, the factors affecting the basal stability of excavation are analyzed and utilized by the program, including the support position, the construction load, the pile length and cohesion of soil layer at pile bottom. The results show that the construction load has little effect on the stability coefficient. And the closer the bottom steel support is to the bottom of the excavation, the worse the stability of the excavation is. Moreover, as the length of the pile increases (i.e., the radius of the arc increases), the stability factor increases first and then decreases, and its peak occurs when the pile length is 16 m. In addition, the basal stability of excavation will be increased when the pile bottom is cohesive soil.

Construction and Live Load Behavior of a Skewed Steel I-Girder Bridge

As part of a long-term monitoring project, a two-span continuous steel I-girder bridge (skewed 41° with seat-type abutments) was instrumented and evaluated in the field during construction and after the bridge was in service. This paper discusses data from when the first stage (of a three-stage sequence) was constructed and initially opened to traffic. Girders and cross-frames were instrumented with strain gauges using a data acquisition system with a high sampling frequency (up to 20 Hz). Data collection began just before deck placement, and a series of live load tests was then conducted on the completed Stage I (half of the bridge) using a loaded truck. Three-dimensional finite element analyses were carried out to provide enhanced understanding of bridge behavior. Good agreement was observed between the numerical simulation results and the field monitoring data for both deck placement and live load testing. A slight inconsistency between numerical simulation and field measurement data at one girder section and an adjacent cross-frame indicated an unexpected local site condition, which was confirmed through a targeted field inspection. Live load distribution factors used during design conservatively overestimate bridge girder strong-axis bending response under live load (by around 50%). Maximum flange lateral bending stresses of 6.3 MPa (0.9 kips per square inch [ksi]) and 2.5 MPa (0.4 ksi) were observed during deck placement and truck tests, respectively. In addition, out-of-plane response of 10.6 MPa (1.5 ksi) was observed at girder web plates under concrete dead load.

Centrifugal model tests on the structural response of the shield tunnel when constructing cross passages by mechanical methods

Mechanical methods to construct cross passages between shield tunnels have received growing attention and have been successfully applied in several projects. However, the structural response of the shield tunnels under the construction load when excavating cross passages by mechanical method remains unclear. Centrifugal model tests were conducted in this paper to investigate the mechanical characteristics of the mainline tunnel loaded by two different reaction modes, i.e., back-thrust mode and front-traction mode. The results show that (1) stress concentration occurs at the segments around the opening of cross passages due to the change of the structural type, which may exceed the strength limit of the concrete; (2) the stress concentration was aggravated by the back-thrust load while alleviated by the front-traction load; (3) the back-thrust loading mode intensifies the trend of the horizontal ellipse of the mainline tunnel which is more adverse for shield tunnels. Therefore, the front-traction reaction mode is better for structural stress and deformation when no other supplementary measures are taken.

COMPARATIVE STUDY OF MODIFIED CONSTRUCTION STAGE ANALYSIS AND CONSTRUCTION STAGE ANALYSIS FOR RC BUILDINGS

A significant difference is found in axial shortening of vertical members in tall concrete buildings when analyzed by Construction Stage Analysis considering the effect of creep and shrinkage as compared to the conventional One Step Analysis method. In Construction Stage Analysis the self-weight of structural members, and a load of brick walls along with floor finishing load, gets added sequentially as construction is carried out. In addition to the above loads, construction loads such as the weight of formwork, the weight of wet concrete, staking of materials, and other construction loads of men and machines get imposed on the structure during construction. Also, stagewise reduction of load due to removal of formwork, material staking, and other construction loads of men and machines should also be considered during the analysis with the Construction stage method. The axial shortening of vertical members of RC buildings was analyzed by the Conventional one-step method, Construction Stage method, considering self-weight along with brick wall and floor finishing load as sequential loads. Modified Construction Stage method-in which in addition to self-weight, brick wall, and floor finishing load, above mentioned all loads that appear during construction, were added, and removed sequentially in the analysis, by taking 20,30, and 40 floor RC building models. Modified CSA gives 2.068% to 20.56% lesser axial shortening in comparison to the CSA method. The study also concludes that the difference of axial shortening between Modified CSA & CSA increases from first to a certain floor, after that it reduces till top floor.

COMPARATIVE STUDY OF MODIFIED CONSTRUCTION STAGE ANALYSIS AND CONSTRUCTION STAGE ANALYSIS FOR RC BUILDINGS

A significant difference is found in axial shortening of vertical members in tall concrete buildings when analyzed by Construction Stage Analysis considering the effect of creep and shrinkage as compared to the conventional One Step Analysis method. In Construction Stage Analysis the self-weight of structural members, and a load of brick walls along with floor finishing load, gets added sequentially as construction is carried out. In addition to the above loads, construction loads such as the weight of formwork, the weight of wet concrete, staking of materials, and other construction loads of men and machines get imposed on the structure during construction. Also, stagewise reduction of load due to removal of formwork, material staking, and other construction loads of men and machines should also be considered during the analysis with the Construction stage method. The axial shortening of vertical members of RC buildings was analyzed by the Conventional one-step method, Construction Stage method, considering self-weight along with brick wall and floor finishing load as sequential loads. Modified Construction Stage method-in which in addition to self-weight, brick wall, and floor finishing load, above mentioned all loads that appear during construction, were added, and removed sequentially in the analysis, by taking 20,30, and 40 floor RC building models. Modified CSA gives 2.068% to 20.56% lesser axial shortening in comparison to the CSA method. The study also concludes that the difference of axial shortening between Modified CSA & CSA increases from first to a certain floor, after that it reduces till top floor.

Effect of concrete under continuous load on demoulding time during construction

Based on the current construction progress of each floor of the building, under the action of continuous construction load, the concrete strength at this time is only about 80% of that at the same age without load. It is suggested that when the test block maintained under the same conditions reaches 85% of the design strength, the whole structure is not easy to crack, which is not safe.

Seismic response analysis of concrete-faced rockfill dams with dual mortar contact method

Many high concrete-faced rockfill dams (CFRD) are constructed or planned with high seismic intensity. It is challenging to evaluate the resultant seismic response involving multi-body interactions. In this paper, a dual mortar contact method for multi-process sequential analysis accounting for staged construction, water storage, creep effects and seismic loading is presented. A complete derivation of the strong and weak forms, spatial and temporal discretizations, material and contact non-linearity treatments is provided as a solid basis to incorporate the rockfill constitutive behavior and stable algorithm for thin-walled inter-slab interfaces. The present method based on using nonconforming meshes is validated by the comparisons with conforming meshes and then applied to an ideal CFRD. The issues of post-earthquake extrusion damage, slab–slab separation and slab–cushion separation, which are major concerns in CFRDs, are discussed in detail. The additional extrusion stress of the concrete face during an earthquake can be up to 20 MPa and therefore calls for considerations in the design and safety assessment.

Effect of Jack Thrust Angle Change on Mechanical Characteristics of Shield Tunnel Segmental Linings Considering Additional Constrained Boundaries

With the attitude adjustment of shield machine, the jack thrust angle will change and may lead to great damage to segmental lining structures. In this paper, a three-dimensional refined finite element method is proposed to study the action mechanism and influence of jack thrust angle change on the mechanical characteristics of shield tunnel, considering additional constrained boundaries formed by various construction loads. Firstly, the finite element method is established and verified. Then, a series of analyses is carried out to investigate the mechanical performance of a certain tunnel lining with eleven rings under conditions of different jack thrust angles. An in-depth discussion is conducted on the obtained displacement, deformation, and stress distribution. A quantitative standard is finally gained for controlling the jack thrust angle. The results show that the maximum segment displacement occurs at the lower part of the arch waist of the second ring out of the shield tail, which has little relationship with the attitude adjustment. With the increase of the jack thrust angle, the maximum offset between the rings increases linearly, which is not conducive to the safety of the lining structures. The development direction of the tunnel displacement is opposite to that of the jack thrust deflection. The displacement of the tunnel is most affected by the jack thrust deflection when the shield machine is upward, which is also the most unfavorable situation for the segmental linings. The results in this paper provide novel insights into the effect of jack thrust on shield tunnel.

Field monitoring of vertical stress distribution in GRS-IBS with full-height rigid facings

This paper presents a case study of the first geosynthetic reinforced soil-integrated bridge system (GRS-IBS) with full-height rigid facings in China. Open graded gravel and biaxial geogrid were used for the GRS-IBS. Steel frames and three-dimensional (3D) vegetation nets were used as temporary facing support during construction of the GRS abutments. Full-height rigid facings were cast in place on strip foundations. Field monitoring results of vertical stress distribution for different construction stages and loading conditions are presented and discussed. For both bridge dead load and truck loads, measured incremental vertical stresses under the beam seat increase significantly with increasing elevation, especially for higher applied vertical stress. The calculated incremental vertical soil stresses using the Boussinesq solution are in reasonable agreement with the measured values, while the 2 : 1 stress distribution method overestimates the incremental stresses in the lower section of the abutment. The transferred vertical stresses from bridge load application for the GRS abutment with full-height rigid facing are larger than those for the GRS abutment with modular block facing near the top of the abutment, but are smaller near the bottom.

Technological Features of Construction and Reconstruction of Geotechnical Structures in the Arctic Zone

Production engineering methods and geotechnical instrumentation for the construction and reconstruction of railway beds in high temperatures in the Arctic zone are proposed. High-technology construction facilitates the development of transport infrastructure of the energy-producing industries in the Arctic. The example of the Northern Latitudinal Railway (NLR) highlights the probability of dangerous cryogenic processes and phenomena during works, such as waterlogging and the structural decline of the active soil layer, the development of taliks, and frost cracking, which lead to a decrease in bearing capacity of soil. The features of the construction and production plans used at the sites of railway embankment reconstruction with heavy-duty equipment are outlined. New process control methods have been developed based on the selection of and systematic changes in the parameters of maximum permissible construction loads depending on the results of geotechnical structure monitoring. The structural diagram of high technology for strengthening the weak subgrade soil under the conditions of talik development is substantiated. In order to regulate intensive process parameters, the vehicle fleet needs to be equipped with positioning devices and automation process control systems. The effectiveness of process control in terms of improving the reliability and accelerating roadbed consolidation is substantiated.

Biomechanical Comparison of Three Suspensory Techniques for all Soft Tissue Central Quadriceps Tendon Graft Fixation

PurposeThe purpose of this study was to evaluate three different methods of attachment of continuous loop suspensory cortical preparation of all soft tissue central quad tendon grafts compared to a bone block control for anterior cruciate ligament reconstruction on construct displacement and load to failure.MethodsThirty-two cadaveric central quadriceps tendon (CQT) specimens were harvested, using three clinical techniques for graft fixation: cortical button alone (BTB EB), BTB cortical button with rip-stop suture (BTB RS), and continuous loop cortical button (BTB CL). A control group was also included that consisted of a bone block secured within testing clamps (BTB CON). Specimens were preloaded to 150 N. Tendons were then cyclically loaded between 50 N and 250 N for 1,000 cycles at .5 Hz. Displacement was measured at the point of fixation of the CQT after the 150 N preload, 250 N initial load and every 100th cycle. The specimens were loaded to failure after 1,000 cycles.ResultsThere was a significant increase in displacement from .32 ± .56 mm for the BTB CON to 1.91 ± 1.13 mm for the BTB RS (P = .014) and 3.85 ± 2.32 mm for the BTB CL condition (P = .023). There was no significant increase in displacement for BTB EB (P = .182). Failure occurred for all of the BTB CL and 62.5% of the BTB EB specimens within the first 50 cycles. Twenty-five percent of the BTB CON specimens and 12.5% BTB RS failed at ∼400 and 500 cycles, respectively. Similar failure loads were observed for the BTB CON and the BTB RS (446.4 ± 151.46 N vs 505.74 ± 131.41 N; P = .99) Failure testing was not feasible for the BTB CL and BTB EB preparation methods.ConclusionIn response to cyclic loading, the three all-soft tissue suspensory conditions experienced significantly greater displacement compared to the bone block controls. None of the soft-tissue conditions appeared superior when compared to each other.Clinical RelevanceIt remains unknown which method of soft-tissue suspensory provides optimal fixation. As these autografts become more common, it is essential to evaluate which fixation methods provide superior outcomes

The Influence of Non-synchronous Excavation of Twin Curved Shield Tunnels

The theoretical model of twin curved shield tunnels and refined numerical model considering the characteristics of wedge-shaped segment ring joints were established in this paper. Two construction schemes of taking the inner side or outer side of the twin curved tunnels as the first tunnel were conducted for comparison. Then two main characteristics of curved tunnel construction (over-excavation and yaw excavation loadings) were taken as variables to explore their response to the approaching construction caused by unsynchronized driving of twin curved shield tunnels. The ground surface settlement troughs obtained by the analytical solution and numerical simulation are in good agreement with the monitoring result. On the condition that the curved tunnel at the inner side is taken as the first tunnel, the excavation will intensify the ground settlement and the internal forces of its segment. In the case that the overcutting gap is not of large volume, it is advisable to first excavate the curved tunnel at the outer side, and then construct the curved tunnel at the inner side. The influence of soil loss on the ground disturbance is greater than that of construction loadings. The excessive overcutting gap not only easily induces a sharp increase in the ground vertical displacement, but also may lead to the movement of soil at the inner and middle sides towards the inner side of the curved tunnels, and causes the soil at the outer side to move towards the outer side of the curved tunnels. Remarkably, excessive overcutting gap may lead to large horizontal displacements of the ground surface.

2D and 3D simulations of static response of a geosynthetic reinforced soil bridge abutment

This paper presents two-dimensional (2D) and three-dimensional (3D) numerical simulations of a half-scale geosynthetic reinforced soil (GRS) bridge abutment during construction and bridge load application. The backfill soil was characterized using a nonlinear elastoplastic model that incorporates a hyperbolic stress–strain relationship and the Mohr–Coulomb failure criterion. Geogrid reinforcements were characterized using linearly elastic elements with orthotropic behavior. Various interfaces were included to simulate the interaction between the abutment components. Results from the 2D and 3D simulations were compared with physical model test measurements from the longitudinal and transverse sections of a GRS bridge abutment. Facing displacements and bridge seat settlements for the 2D and 3D simulations agree well with measured values, with the 2D-simulated values larger than the 3D-simulated values due to boundary condition effects. Results from the 3D simulation are in reasonable agreement with measurements from the longitudinal and transverse sections. The 2D simulation can also reasonably capture the static response of GRS bridge abutments and is generally more conservative than the 3D simulation.

Load-Effect Separation of a Large-Span Prestressed Structure Based on an Enhanced EEMD-ICA Methodology

Prestressed structures have gained popularity in large-span buildings due to their great spanning capacity and light self-weights. This kind of structure is normally subjected to multiple types of loads, such as temperature load, wind load, and construction load. The determination of different load effects not only guides the design of similar structures but also helps reveal the damage-induced variation that would be concealed by the environmental loads. To determine the different load effects, separation of the load effects collected by structural health monitoring (SHM) is needed. This study presents an enhanced approach for load effect separation based on independent component analysis (ICA) and ensemble empirical mode decomposition (EEMD), called EEMD-ICA*. The proposed method is to minimize manual tuning of user-defined parameters, which makes the EEMD-ICA suitable for separating load effects from the different measured data. Specifically, an optimization method is developed to determine the appropriate level of the added white noise in the EEMD using the relative root-mean-square error (RMSE) index. A logarithm form of Bayesian information criterion (BIC) is employed for the robust estimation of the number of load effects in the ICA. Simulated structural responses from a square orthogonal cable-net are used to validate the effectiveness of the EEMD-ICA*. Then, the proposed methodology is employed to extract various load effects from the SHM data of the National Speed Skating Oval (NSSO), which is the largest single-layer cable-net structure in the world.

Collagen X Longitudinal Fracture Biomarker Suggests Staged Fixation in Tibial Plateau Fractures Delays Rate of Endochondral Repair.

To use a novel, validated bioassay to monitor serum concentrations of a breakdown product of collagen X in a prospective longitudinal study of patients sustaining isolated tibial plateau fractures. Collagen X is the hallmark extracellular matrix protein present during conversion of soft, cartilaginous callus to bone during endochondral repair. Previous preclinical and clinical studies demonstrated a distinct peak in collagen X biomarker (CXM) bioassay levels after long bone fractures. Level 1 academic trauma facility. Thirty-six patients; isolated tibial plateau fractures. (3) Closed treatment, ex-fix (temporizing/definitive), and open reduction internal fixation. Collagen X serum biomarker levels (CXM bioassay). Twenty-two men and 14 women (average age: 46.3 y; 22.6-73.4, SD 13.3) enrolled (16 unicondylar and 20 bicondylar fractures). Twenty-five patients (72.2%) were treated operatively, including 12 (33.3%) provisionally or definitively treated by ex-fix. No difference was found in peak CXM values between sexes or age. Patients demonstrated peak expression near 1000 pg/mL (average: male-986.5 pg/mL, SD 369; female-953.2 pg/mL, SD 576). There was no difference in peak CXM by treatment protocol, external fixator use, or fracture severity (Schatzker). Patients treated with external fixation (P = 0.05) or staged open reduction internal fixation (P = 0.046) critically demonstrated delayed peaks. Pilot analysis demonstrates a strong CXM peak after fractures commensurate with previous preclinical and clinical studies, which was delayed with staged fixation. This may represent the consequence of delayed construct loading. Further validation requires larger cohorts and long-term follow-up. Collagen X may provide an opportunity to support prospective interventional studies testing novel orthobiologics or fixation techniques. Level II, prospective clinical observational study.

Technological regulation and monitoring of roadbed construction

Background: Long-term deformations of hydraulic structures on weak foundations and swamps lead to the need to develop new construction technologies that increase the bearing capacity of soils. The existing standards for the design of railways and highways are mainly focused on ensuring the safety of the roadbed at the operational stage. Meanwhile, the risks of loss of stability and stability of road sections also arise at the construction stage, especially when powerful heavy construction machinery and equipment are operating.
 Aim: Formation of a technical and technological system functioning on the principles of direct and feedback between the characteristics of the constructed roadbed and the parameters of construction equipment to ensure the safety and quality of work.
 Methods: Technological regulation of loads and impacts of construction machinery and equipment during the strengthening of the foundation and the construction of embankments of the roadbed.
 Results: The composition of the complex technology and the regime of regulation of construction loads have been developed to increase the bearing capacity of weak soils at the base of the roadbed of railways and highways. The features of geotechnical monitoring for the directed improvement of the strength characteristics of soils during the construction period are determined. The expediency of technological regulation of loads and impacts of construction machinery, equipment during the construction of the roadbed is shown.
 Conclusion: The complex technology of increasing the load-bearing capacity of the weak foundation of the roadbed consists in the consistent application of regulated modes of intensive impact on each layer of the foundation with the maximum permissible load during geotechnical monitoring.

Monitoring land subsidence using interferometric synthetic aperture radar time-series analysis: a case of Shanghai Pilot Free Trade Zone

Shanghai Pilot Free Trade Zone (SPFTZ) is the first free trade zone in China, consisting of eight independent zones and located in Pudong New District. With the rapid development in the SPFTZ, frequent human activities may induce severe land subsidence. Based on time-series interferometric synthetic aperture radar (InSAR) technique and multitemporal C-band images, the temporal and spatial evolution of subsidence in Pudong New District is obtained from May 2016 to October 2020. The achieved results show that severe subsidence occurred in the east of the study area, where the maximum subsidence rate was −40 mm / year. Most of the land in the SPFTZ remained stable, but small-scale subsidence with a maximum subsidence rate of −18.1 mm / year occurred in two zones. InSAR-derived results are in good agreement with the manual measurements, with a root mean square error of 1.4 mm. Time-series analysis reveals that land subsidence in the SPFTZ mainly originates from urban constructions, including building construction and vehicle load. Meanwhile, the most severe subsidence occurred in the east of Pudong International Airport, which may be attributed to the airport renovation project. In a reclaimed area, land subsidence can be classified into different construction periods, which gradually weakens from north to south.

Load Deflection Relationship of a Solid Slab under the Action of Construction Loads

Over the past decades, there has been a tremendous improvement in the concrete placement technology in Uganda. The methods have moved from being manual to the use of concrete pumps. A concrete pump is capable of pumping high volumes of concrete per minute. This implies that for small volume slabs before the setting of concrete, the whole weight of the fresh concrete of the upper slab, formwork, and props is transferred to the lower supporting slab. During construction, slabs are stacked with materials like bricks, blocks, sand, and aggregates. Construction loads such as block loads and loads due to props, formwork, and freshly cast solid concrete slabs on the lower floor are usually greater than the imposed loads and are not catered for in design. A baseline survey carried out on 118 randomly selected sites in Kampala revealed that in 87% of the cases, supports are removed from a lower reinforced concrete slab, and then props are put on its top to support a yet to be cast slab on an upper floor. It also revealed that 80.6% of the slabs had construction loads such as bricks, blocks, sand, timber, and aggregates. Deflections were measured using dial gauges for construction loads owing to freshly cast slab and concrete blocks in a physical model of a multistory structure with dimensions of 4 m long, 2 m wide, 2 m high to 2nd level, and 2 m to 3rd level. Loads due to freshly cast concrete were 158% more than unfactored design live loads. The maximum deflection at center of the slab due to a freshly cast slab and blocks loaded instantly was 1.15 mm and 11.815 mm, respectively, compared to the immediate deflection equal to 0.103 mm due to a design‐imposed load of 2 KN/m2.

Properties of aerated concrete with steel sludge waste from automobile industry

Research on new materials based on the current construction scenario for different applications has led to development of many special concretes. Lightweight concrete is one such type which has many advantages like reduced dead load, thermal comfort and economy in construction. But the major disadvantage that has restricted the popularity of its use is the low compressive strength. This work is based on developing a lightweight concrete by way of making it a sustainable construction material developed from waste steel sludge generated in automobile industry. The compressive and flexural strength of this concrete was 22 MPa and 1.8 MPa respectively. Durability properties were also studied proving that the material can be used in construction. Microstructure investigations were done to analyze the porosity of the concrete and the products formed during the hydration reaction. The total experimental sequence was designed using response surface methodology of central composite design and the experimental results were analyzed by ANOVA to find the significance of the parameters. Response surface graphs and optimization was obtained as a result of the experimental results.