Academic literature on the topic 'High Rise Steel Structures'

With the increased demand for high-rise and long-span structures, high strength with high performance steels have been utilized for these kind of structures. For the grade 800MPa high performance steel, although it was included in Korean Standard as high strength steel(HSA 800), however the HSA 800 steel was excluded in Korean Building Code-Structures due to the rack of research results for the structural behaviors of members fabricated with HSA 800 steel. Therefore, this paper describes basic study for the design specification of structural members using HSA 800 high performance steel. For this purpose, welded H-shaped stub column specimens with various width-to-thickness ratios were designed and tested in order to investigate the buckling behaviors and ultimate compressive strength.

The earthquake responses of short span structures are usually obtained by using uniform excitations. Wave passage effects are often artificially neglected for short span structures. In this paper, a high-rise steel residence structure of 18-story is adopted to study the earthquake responses of high-rise steel structures to wave passage excitations and uniform excitations by using the software Midas/GEN. Two groups of earthquake acceleration records are chosen respectively from sites of hard soil and soft soil. Comparisons of the shear forces and the bending moments under uniform excitations and wave passage excitations shown that wave passage effects shouldn’t be neglected in the earthquake response analyses even for short span structures.

In recent years, due to its excellent mechanical properties, especially its insensitivity of strength to thickness, high-rise structural steel with high performance and heavy thickness made in china was applied more and more widely in large-span and high-rise steel building structures. However, there are no reasonable design indexes based on design reliability analysis for the new material in relevant national standards. The high-rise structural steel was often used as H-section column with heavy thickness at present, and its residual stress distribution has significant influence on load-carrying capacity, which is one of the critical factors in reliability analysis of elementary members using high-rise structural steel. In this paper, with the block sectioning method, a detailed experimental investigation on the longitudinal residual stress distribution for H-section (H800×800×80×80mm), made from Q345GJ high-rise structural steel with thickness of 80mm is introduced. The contour of residual stress distribution in the whole section based on test was presented, and the regularity of the residual stress distribution of such a section was discussed. Meanwhile, the contour of yielding strength distribution in the whole H-shaped section with heavy thickness was obtained. It will provide some basic data for reliability analysis and further investigation of the structural members using high-rise structural steel.

During earthquake, the ground along with its various natural and manmade structures experiences shaking of various intensities and frequencies depending on the nature of the earthquake. The loading activities caused by earthquakes on various structures are very much cyclic type, which is popularly known as fatigue loading. On the other hand, for modern high-rise buildings a large volume of steel bar is used to reinforce the concrete because of the pioneer role of steel bars embedded inside the concrete for safety of the buildings. In this study various mechanical properties of reinforcing steel bars that are essential to counter balance the earthquake effects have been identified first. At the same time these essential mechanical properties have been defined and studied for most commonly used reinforcing steel bars. For doing this, both the conventional and advanced structural steels were selected. The mechanical properties and fatigue behaviours of these steels have been presented and discussed in this paper. Keywords: Earthquake; High-rise buildings; Reinforcing steel bars; Conventional structural steel; Advanced structural steel.© 2012 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.doi: http://dx.doi.org/10.3329/jsr.v4i1.7069 J. Sci. Res. 4 (1), 51-63 (2012)

In order to properly design critical infrastructures and buildings in steel (bridges, high-rise building, off-shore, cranes, etc.), certain requirements concerning to mechanical resistance and robustness under exceptional actions have to be carefully fulfilled. An acceptable level of safety must be assured to avoid human loss, environmental pollution and material damage. These structures can be subjected to severe accidental loading such as blast or impact. In this context it is fundamental to adequately know the behaviour of structural steel under high strain rate. Modern high strength steels are quenched and selftempered steels. These steels have several layers with differentiated microstructures (martensitic in the cortical part and ferritic in the core). The behaviour of the single layer at high strain rate regimes have to be accurately studied. The paper collects and discusses the tensile results at high strain rate obtained on samples of homogeneous layers of S690QL and S960QL steels. Finally, the characterisation of the single layers has been used in order to analyse the results obtained in large specimen obtained from slabs 12mm thick.

High-rise buildings have a specificity, which significantly distinguishes them from traditional buildings of high-rise and multi-storey buildings. Steel structures in high-rise buildings are advisable to be used in earthquake-proof regions, since steel, due to its plasticity, provides damping of the kinetic energy of seismic impacts. These aspects should be taken into account when choosing a structural scheme of a high-rise building and designing load-bearing structures. Currently, modern regulatory documents do not quantify the reliability of structures. Although the problem of assigning an optimal level of reliability has existed for a long time. The article shows the possibility of designing metal structures of high-rise buildings with specified reliability. Currently, modern regulatory documents do not quantify the reliability of high-rise buildings. Although the problem of assigning an optimal level of reliability has existed for a long time. It is proposed to establish the value of reliability 0.99865 (3σ) for constructions of buildings and structures of a normal level of responsibility in calculations for the first group of limiting states. For increased (construction of high-rise buildings) and reduced levels of responsibility for the provision of load-bearing capacity, it is proposed to assign respectively 0.99997 (4σ) and 0.97725 (2σ). The coefficients of the use of the cross section of a metal beam for different levels of security are given.

The “Lakhta Center” skyscraper that built up in Saint-Petersburg on the coast of Baltic sea at the end of 2018 is the highest building of Europe. The tower has 87 floors above the ground and 2 underground floors. The distinctive paper is devoted to structures of this skyscraper. Particularly piled foundation, building structures of the underground part (substructure), building structures of the aboveground part (building superstructure), de­signs of steel-reinforced concrete columns, design of slabs, structural analysis, some loads and impacts, aerody­namic tests, engineering-geological research, testing of steel-reinforced concrete columns, glass racks and struc­tural health monitoring are under consideration.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2006.
Includes bibliographical references.
Selecting a structural system for a building is a complex, multidisciplinary process. No design project is the same; however, there are certain criteria that are commonly true in the initial phase of evaluating different structural schemes. These criteria encompass all aspects of a full, functioning building, forcing the design team to be creative in their approach of satisfying all facets. An investigation was carried out for several structural steel framing options available to designers. The schemes describe how each successfully resist lateral loads explaining the advantages and disadvantages of each. Many of the structural design tools available for initial structural system evaluation are strength based. The demand for cheaper, more efficient and taller structures has paved the way for performance based design. A simple cantilever beam performance based analysis was utilized to evaluate three common structural framing schemes in order to gain a better understanding of the performance of each. Results give recommendations for efficient structural solutions for proposed buildings as a function of height.
by Jason A. Cook.
M.Eng.

Vi har valt att undersöka vilka möjligheter och eventuella risker det finns att bygga högt i Stockholm. Undersökningen utgick på att jämföra olika byggtekniska lösningar för stomsystem. Hur tar stomsystemen hand om vertikala och horisontella laster? Vilket stomsystemen är lämpligast vid en viss höjd? Dessa är några av de frågor som besvaras i arbetet. De vertikala och horisontella lasterna är de faktorer som främst försvårar höghusbyggandet. Med en större belastning av laster ju högre det byggs måste stomsystemen dimensioneras med allt större noggrannhet för att lasterna ska nedföras till grundläggningen på ett säkert sätt. Stomsystemen måste även dimensioneras för de svajningar och stabilitetsproblem som uppstår av de transversella lasterna. Genom inläsning av litteratur och intervjuer angående ämnet så har vi kommit fram till att den största orsaken att det finns så få höghus i Sverige beror på den politiska inställningen i landet och efter Turning Torsos kostnad dubblerades så har många dragit sig undan höghusprojekt. Byggtekniskt har vi i Sverige erfarenheter att bygga upp till 100-150m.
We have in this thesis decided to examine the possibilities and the possible hazards of high-rise buildings in Stockholm. We compared the different structural systems to determine how the systems handle the vertical and transversal loads and which system is to recommend to a certain height. The vertical and transversal loads are the main factors that make high-rise buildings harder to dimension than normal buildings. The higher the building is the more vertical and transversal loads that needs to be accounted in the dimensioning of the structural systems. This needs to be done accurately to secure the safety of the building. The sway and stability problems that occurs from the transversal loads need to be taking into account when designing the structural system. By reading literature and conducting interviews about the subject we can come to the conclusion that the reason why Sweden is behind with recent high-rise development is because of political reasons rather than lack of knowledge. We in Sweden have the experience to successfully build high-rise buildings up to 100-150m.

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2003.
Includes bibliographical references (leaves 47-48).
by Christopher D. Lubke.
M.Eng.

Comparative performance evaluation including life cycle cost is currently being conducted on a series of conventional and base-isolated case study buildings. Alternative design approaches and their influence in cost were to be evaluated . This investigation is intended to contribute in the development of isolated structures by allowing engineers to communicate the cost of higher performance systems to their clients. The reported effort is part of a larger cost-benefit study for isolated steel buildings, and the purpose of this thesis is to compare initial investment of 3-story conventional and isolated steel buildings and determine how isolation affects the cost of the structure. The relative cost of seismic isolation, as a percentage of the total cost, may be higher in this study than for typical U.S. isolation applications because the relative premium is greater for a short building than a tall building. The cost of isolation layer for this building is in the order of 11.7% to 12.4% of the total cost. Such a large cost premium may be a huge restraint for most owners; therefore, strategies to reduce the isolation premium cost need to be investigated in detail.

Timber-steel hybrid systems utilize timber as main construction material, but also take advantage of the ductility and stiffness that steel provides. For a novel hybrid system to gain recognition, experimental data must be supported by numerical analysis to predict its structural performance. “Finding the Forest Through the Trees” (FFTT) is one proposal for a timber-steel hybrid system using mass-timber panels as shear walls and floor slabs connected with steel header beams. This thesis presents research to evaluate the seismic performance of the FFTT hybrid system using experimental methods, numerical modeling, and reliability analysis. The FFTT system was investigated on two levels: i) component design, and ii) system design. On the component level, the strength, stiffness, ductility, and failure mechanisms of the two key connections were evaluated experimentally. CLT (Cross Laminated Timber) wall to steel beam connection tests results demonstrated that appropriate connection layouts can lead to the desired failure mechanism while avoiding crushing of the mass-timber panels. For the hold-down connection, a modified HSK (Holz-Stahl-Komposit) assembly with high force and stiffness capacity together with ductile behaviour was proposed. On the system level, the seismic response of the FFTT system with different ductility values was investigated using nonlinear 2D and 3D models subjected to a number of ground motion acceleration records. The seismic reliability with various uncertainties was analysed in order to investigate the FFTT system from a performance based approach. Based on the results, an appropriate seismic force reduction factor specific to the FFTT system was proposed. Finally, a feasibility study confirmed the possibility of the practical application of this system. This thesis can serve as a precursor for developing design guidelines for tall wood-hybrid building systems in seismic regions.
Forestry, Faculty of
Graduate

This dissertation reports a case study in the design and construction solutions for a major corrosion failure of the aluminium louvres and steel brackets on the roof and fa??ade of levels 26-29 of the Westfield Tower 2, Bondi Junction. This work was undertaken during early 2005. Aims: ?? Consideration of the roles and responsibilities of designer and engineer working on metallurgical corrosion issues in high-rise buildings ?? Undertaking of a literature survey of corrosion issues involving riveting and welding of aluminium and galvanising of steel ?? Undertaking of stress calculations for all components to ensure compliance with the requirements of design principles ?? Confirmation of the stress calculations through finite element modelling ?? Examination of all materials issues in order to prevent re-occurrence of structural degradation and corrosion ?? Consideration of relevant environmental effects on the materials ?? Implementation of these design solutions using novel aerospace materials and methods ?? Prediction of future performance through factorial and matrix method approaches Outcomes: ?? It is hoped that the text provides a documentary basis for future guidance of designers and engineers working in areas related to the subject of the present work. ?? It also is hoped that the work on aerospace technologies will broaden the scope of designers and engineers in the potential that these materials and processes have in building considerations. ?? The manual stress calculations and finite element modelling confirm that the implemented designs are consistently within design specification and that, from the mechanical perspective, no problems are anticipated. ?? Further, since considerable care was taken to ensure that galvanic and other forms of corrosion were avoided through the appropriate use of design, materials, and implementation approaches, no further corrosion has been observed at the site. ?? The development of a generic factorial approach and a specific matrix method, applied to corrosion and welding considerations, was informative but these still are at speculative stages owing to the difficulty of obtaining relevant meaningful data and the problem of assigning weighting factors on what is viewed as a fairly subjective basis.

<p>New steel production processes have led to a remarkable improve­ment in steel products within the last few years, and now allows steels to be produced according to the desired mechanical and chemical properties. High-Performance Steel (HPS) is the designa­tion given to this new generation of steels that offer higher performance not only in terms of strength but also toughness, weld­ability, cold formability and corrosion resistance, compared to the traditionally used mild steel grades.</p> <p>The development of HPS goes with today's increased demand for slender lightweight structures, as for example in bridge design and the design of high-rise buildings, where there is a strong require­ment to use high-strength materials in combination with good execution and fabrication properties. However, on the structural engineering side there is a need for knowledge on these new steel grades, and quite often design codes do not provide sufficient information to fully exploit the advantageous properties of HPS.</p> <p>The present volume provides an overview of the development and application of HPS on an international level. This is done by giving information on, for example, the production process, the chemical and mechanical properties, the relevant design and fabrication standards and on recent research results. Approximately fifteen included examples of realised applications aim to provide detailed information based on existing technical solutions, and to point out the major benefits when using HPS in comparison to mild steels.</p> <p>The document is thus not a monograph but an assembly of contri­butions from different countries. lt is separated into chapters related to different countries, namely the USA, Canada, Japan and Europe, all of them providing a state-of-the-art report on HPS.</p>

Modular construction has gained popularity and attention particularly in low-rise building lately due to its numerous advantages: faster construction speed, better quality control, reduction in work force and construction waste, etc. This innovative technology promotes off-site manufacturing of modular units and on-site assembly, improving the construction efficiency and productivity. However, modular construction is not commonly used in high-rise buildings because of the joints’ flexibility as well as manufacturing and construction tolerance, which have significant impact on the overall stability of the building. This paper highlights the existing challenges of modular construction of high-rise buildings and provide several options to address these challenges. Firstly, the weight of a module is constrained by the transportation and lifting crane capacities. For this reason, lightweight concrete is introduced together with structural steel section to form lightweight steel-concrete composite system to reduce the weight of the module without compromising the strength and stiffness. Secondly, to speed up the site assembly of modular units, special joints are developed to resist the forces due to gravity and horizontal loads. Fast and easy joining techniques with acceptable tolerance control are essential to ensure the structural integrity and stability of the building. Finally, the innovation for productivity can be maximized by implementing automation technologies in the manufacturing and construction of the modular units.

Due to the safety awareness arisen from natural and human-caused disasters, robustness design of building is increasingly important to ensure the stability of the building and to prevent progressive collapse. For this reason, the robustness design of innovative construction technologies such as modular construction may be essential due to its relative novel structural form and numerous joints among modules. Particularly in Singapore, Prefabricated Prefinished Volumetric Construction (PPVC) has been highly promoted in residential and commercial buildings, hostels and hospitals to boost the construction productivity and quality as well as to reduce the reliance on foreign workforce. PPVC offers high quality and efficiency because most of the finishes and mechanical and electrical services are manufactured and installed together with the modules in factory, before sending for on-site assembly. To maximize the productivity of PPVC, modular design standardization and repetition can be improved by going for high-rise. Nonetheless, there are limited studies on the robustness of PPVC high-rise building and its behavior under progressive collapse remains uncertain. Therefore, this paper investigates the robustness of steel PPVC high-rise building under column removal scenarios by conducting non-linear numerical analysis. The effects of joint design and diaphragm action between modules are studied to ensure continuity of horizontal and vertical tying. This paper provides insight on the behaviour and alternative path for load transfer under column removal scenario for future design guideline of robustness PPVC building.

In recent years, there is rapid increase in the construction of high rise structures due to the increase in population, high cost of land and restriction in horizontal growth due to less space. The advancements in the development of technological solutions and construction methods of high rise structures led to the innovative structural systems. One of the important criteria that need to be considered in the design of high rise structures is minimization of lateral loads. Hence, the importance of lateral load resisting system increased than structural systems that resist gravitational loads. Lateral loading due to wind and earthquake are the major factors that have to be considered in the design of high-rise structures. Diagrid structural system is recognized as a unique system in construction of high rise structures which is a variation of tubular structures. It consists of inclined members instead of vertical columns in conventional structures to carry both gravity and lateral loads. It gains popularity due to its structural efficiency and aesthetic potential gained by its unique geometric configuration. The present work reviews studies regarding seismic performance assessment of steel diagrid structures, studies on seismic performance factors of steel diagrid structures, impact of shear-lag effect and comparative studies on diagrids. Diagrids are found to be an efficient structural system for high rise structures in terms of structural efficiency as well as aesthetics. Also, it provides more economy, in terms of consumption of steel, thus making it cost-effective and eco-friendly.

All structures in Switzerland - that is, all buildings, roads, infrastructure constructions and so on - consume over their entire life cycle around 50 % of Switzerland's final energy requirement. They are also responsible for around 30 % of emissions of the greenhouse gas CO2. In recent decades, the energy requirements and CO2 emissions resulting from the use of such structures have fallen sharply. However, the grey energy contained within the structures as well as the CO2 emissions associated with the construction, renovation and demolition of buildings, remain high. There is great potential for improvement here. The joint project “Low energy concrete” provides an important basis for transforming the construction industry into a sustainable sector. It primarily focuses on the building material concrete, which is responsible for an especially high amount of grey energy and significant CO2 emissions. The results of this joint project are summarised and interpreted in this synthesis on “Sustainable Concrete Structures”. The chief objectives of the joint project were as follows: CO2 emissions and grey energy are reduced by drastically decreasing the amount of clinker in the cement. Grey energy is reduced by replacing reinforcing and prestressing steel in concrete structures with wood and plastic. The service life of the structures is extended by professional monitoring and adequate renovation measures; this reduces the average annual grey energy and CO2 emissions. The research work shows that the CO2 emissions caused by concrete and concrete structures can be reduced by a factor of 4, while the bound grey energy can be decreased by a factor of 3.

This report presents a wave method to be used for the structural identification and damage detection of structural components in bridges, e.g., bridge piers. This method has proven to be promising when applied to real structures and large amplitude responses in buildings (e.g., mid-rise and high-rise buildings). This study is the first application of the method to damaged bridge structures. The bridge identification was performed using wave propagation in a simple uniform shear beam model. The method identifies a wave velocity for the structure by fitting an equivalent uniform shear beam model to the impulse response functions of the recorded earthquake response. The structural damage is detected by measuring changes in the identified velocities from one damaging event to another. The method uses the acceleration response recorded in the structure to detect damage. In this study, the acceleration response from a shake-table four-span bridge tested to failure was used. Pairs of sensors were identified to represent a specific wave passage in the bridge. Wave velocities were identified for several sensor pairs and various shaking intensities are reported; further, actual observed damage in the bridge was compared with the detected reductions in the identified velocities. The results show that the identified shear wave velocities presented a decreasing trend as the shaking intensity was increased, and the average percentage reduction in the velocities was consistent with the overall observed damage in the bridge. However, there was no clear correlation between a specific wave passage and the observed reduction in the velocities. This indicates that the uniform shear beam model was too simple to localize the damage in the bridge. Instead, it provides a proxy for the overall extent of change in the response due to damage.

1.1 Macroeconomic summary Economic recovery has consistently outperformed the technical staff’s expectations following a steep decline in activity in the second quarter of 2020. At the same time, total and core inflation rates have fallen and remain at low levels, suggesting that a significant element of the reactivation of Colombia’s economy has been related to recovery in potential GDP. This would support the technical staff’s diagnosis of weak aggregate demand and ample excess capacity. The most recently available data on 2020 growth suggests a contraction in economic activity of 6.8%, lower than estimates from January’s Monetary Policy Report (-7.2%). High-frequency indicators suggest that economic performance was significantly more dynamic than expected in January, despite mobility restrictions and quarantine measures. This has also come amid declines in total and core inflation, the latter of which was below January projections if controlling for certain relative price changes. This suggests that the unexpected strength of recent growth contains elements of demand, and that excess capacity, while significant, could be lower than previously estimated. Nevertheless, uncertainty over the measurement of excess capacity continues to be unusually high and marked both by variations in the way different economic sectors and spending components have been affected by the pandemic, and by uneven price behavior. The size of excess capacity, and in particular the evolution of the pandemic in forthcoming quarters, constitute substantial risks to the macroeconomic forecast presented in this report. Despite the unexpected strength of the recovery, the technical staff continues to project ample excess capacity that is expected to remain on the forecast horizon, alongside core inflation that will likely remain below the target. Domestic demand remains below 2019 levels amid unusually significant uncertainty over the size of excess capacity in the economy. High national unemployment (14.6% for February 2021) reflects a loose labor market, while observed total and core inflation continue to be below 2%. Inflationary pressures from the exchange rate are expected to continue to be low, with relatively little pass-through on inflation. This would be compatible with a negative output gap. Excess productive capacity and the expectation of core inflation below the 3% target on the forecast horizon provide a basis for an expansive monetary policy posture. The technical staff’s assessment of certain shocks and their expected effects on the economy, as well as the presence of several sources of uncertainty and related assumptions about their potential macroeconomic impacts, remain a feature of this report. The coronavirus pandemic, in particular, continues to affect the public health environment, and the reopening of Colombia’s economy remains incomplete. The technical staff’s assessment is that the COVID-19 shock has affected both aggregate demand and supply, but that the impact on demand has been deeper and more persistent. Given this persistence, the central forecast accounts for a gradual tightening of the output gap in the absence of new waves of contagion, and as vaccination campaigns progress. The central forecast continues to include an expected increase of total and core inflation rates in the second quarter of 2021, alongside the lapse of the temporary price relief measures put in place in 2020. Additional COVID-19 outbreaks (of uncertain duration and intensity) represent a significant risk factor that could affect these projections. Additionally, the forecast continues to include an upward trend in sovereign risk premiums, reflected by higher levels of public debt that in the wake of the pandemic are likely to persist on the forecast horizon, even in the context of a fiscal adjustment. At the same time, the projection accounts for the shortterm effects on private domestic demand from a fiscal adjustment along the lines of the one currently being proposed by the national government. This would be compatible with a gradual recovery of private domestic demand in 2022. The size and characteristics of the fiscal adjustment that is ultimately implemented, as well as the corresponding market response, represent another source of forecast uncertainty. Newly available information offers evidence of the potential for significant changes to the macroeconomic scenario, though without altering the general diagnosis described above. The most recent data on inflation, growth, fiscal policy, and international financial conditions suggests a more dynamic economy than previously expected. However, a third wave of the pandemic has delayed the re-opening of Colombia’s economy and brought with it a deceleration in economic activity. Detailed descriptions of these considerations and subsequent changes to the macroeconomic forecast are presented below. The expected annual decline in GDP (-0.3%) in the first quarter of 2021 appears to have been less pronounced than projected in January (-4.8%). Partial closures in January to address a second wave of COVID-19 appear to have had a less significant negative impact on the economy than previously estimated. This is reflected in figures related to mobility, energy demand, industry and retail sales, foreign trade, commercial transactions from selected banks, and the national statistics agency’s (DANE) economic tracking indicator (ISE). Output is now expected to have declined annually in the first quarter by 0.3%. Private consumption likely continued to recover, registering levels somewhat above those from the previous year, while public consumption likely increased significantly. While a recovery in investment in both housing and in other buildings and structures is expected, overall investment levels in this case likely continued to be low, and gross fixed capital formation is expected to continue to show significant annual declines. Imports likely recovered to again outpace exports, though both are expected to register significant annual declines. Economic activity that outpaced projections, an increase in oil prices and other export products, and an expected increase in public spending this year account for the upward revision to the 2021 growth forecast (from 4.6% with a range between 2% and 6% in January, to 6.0% with a range between 3% and 7% in April). As a result, the output gap is expected to be smaller and to tighten more rapidly than projected in the previous report, though it is still expected to remain in negative territory on the forecast horizon. Wide forecast intervals reflect the fact that the future evolution of the COVID-19 pandemic remains a significant source of uncertainty on these projections. The delay in the recovery of economic activity as a result of the resurgence of COVID-19 in the first quarter appears to have been less significant than projected in the January report. The central forecast scenario expects this improved performance to continue in 2021 alongside increased consumer and business confidence. Low real interest rates and an active credit supply would also support this dynamic, and the overall conditions would be expected to spur a recovery in consumption and investment. Increased growth in public spending and public works based on the national government’s spending plan (Plan Financiero del Gobierno) are other factors to consider. Additionally, an expected recovery in global demand and higher projected prices for oil and coffee would further contribute to improved external revenues and would favor investment, in particular in the oil sector. Given the above, the technical staff’s 2021 growth forecast has been revised upward from 4.6% in January (range from 2% to 6%) to 6.0% in April (range from 3% to 7%). These projections account for the potential for the third wave of COVID-19 to have a larger and more persistent effect on the economy than the previous wave, while also supposing that there will not be any additional significant waves of the pandemic and that mobility restrictions will be relaxed as a result. Economic growth in 2022 is expected to be 3%, with a range between 1% and 5%. This figure would be lower than projected in the January report (3.6% with a range between 2% and 6%), due to a higher base of comparison given the upward revision to expected GDP in 2021. This forecast also takes into account the likely effects on private demand of a fiscal adjustment of the size currently being proposed by the national government, and which would come into effect in 2022. Excess in productive capacity is now expected to be lower than estimated in January but continues to be significant and affected by high levels of uncertainty, as reflected in the wide forecast intervals. The possibility of new waves of the virus (of uncertain intensity and duration) represents a significant downward risk to projected GDP growth, and is signaled by the lower limits of the ranges provided in this report. Inflation (1.51%) and inflation excluding food and regulated items (0.94%) declined in March compared to December, continuing below the 3% target. The decline in inflation in this period was below projections, explained in large part by unanticipated increases in the costs of certain foods (3.92%) and regulated items (1.52%). An increase in international food and shipping prices, increased foreign demand for beef, and specific upward pressures on perishable food supplies appear to explain a lower-than-expected deceleration in the consumer price index (CPI) for foods. An unexpected increase in regulated items prices came amid unanticipated increases in international fuel prices, on some utilities rates, and for regulated education prices. The decline in annual inflation excluding food and regulated items between December and March was in line with projections from January, though this included downward pressure from a significant reduction in telecommunications rates due to the imminent entry of a new operator. When controlling for the effects of this relative price change, inflation excluding food and regulated items exceeds levels forecast in the previous report. Within this indicator of core inflation, the CPI for goods (1.05%) accelerated due to a reversion of the effects of the VAT-free day in November, which was largely accounted for in February, and possibly by the transmission of a recent depreciation of the peso on domestic prices for certain items (electric and household appliances). For their part, services prices decelerated and showed the lowest rate of annual growth (0.89%) among the large consumer baskets in the CPI. Within the services basket, the annual change in rental prices continued to decline, while those services that continue to experience the most significant restrictions on returning to normal operations (tourism, cinemas, nightlife, etc.) continued to register significant price declines. As previously mentioned, telephone rates also fell significantly due to increased competition in the market. Total inflation is expected to continue to be affected by ample excesses in productive capacity for the remainder of 2021 and 2022, though less so than projected in January. As a result, convergence to the inflation target is now expected to be somewhat faster than estimated in the previous report, assuming the absence of significant additional outbreaks of COVID-19. The technical staff’s year-end inflation projections for 2021 and 2022 have increased, suggesting figures around 3% due largely to variation in food and regulated items prices. The projection for inflation excluding food and regulated items also increased, but remains below 3%. Price relief measures on indirect taxes implemented in 2020 are expected to lapse in the second quarter of 2021, generating a one-off effect on prices and temporarily affecting inflation excluding food and regulated items. However, indexation to low levels of past inflation, weak demand, and ample excess productive capacity are expected to keep core inflation below the target, near 2.3% at the end of 2021 (previously 2.1%). The reversion in 2021 of the effects of some price relief measures on utility rates from 2020 should lead to an increase in the CPI for regulated items in the second half of this year. Annual price changes are now expected to be higher than estimated in the January report due to an increased expected path for fuel prices and unanticipated increases in regulated education prices. The projection for the CPI for foods has increased compared to the previous report, taking into account certain factors that were not anticipated in January (a less favorable agricultural cycle, increased pressure from international prices, and transport costs). Given the above, year-end annual inflation for 2021 and 2022 is now expected to be 3% and 2.8%, respectively, which would be above projections from January (2.3% and 2,7%). For its part, expected inflation based on analyst surveys suggests year-end inflation in 2021 and 2022 of 2.8% and 3.1%, respectively. There remains significant uncertainty surrounding the inflation forecasts included in this report due to several factors: 1) the evolution of the pandemic; 2) the difficulty in evaluating the size and persistence of excess productive capacity; 3) the timing and manner in which price relief measures will lapse; and 4) the future behavior of food prices. Projected 2021 growth in foreign demand (4.4% to 5.2%) and the supposed average oil price (USD 53 to USD 61 per Brent benchmark barrel) were both revised upward. An increase in long-term international interest rates has been reflected in a depreciation of the peso and could result in relatively tighter external financial conditions for emerging market economies, including Colombia. Average growth among Colombia’s trade partners was greater than expected in the fourth quarter of 2020. This, together with a sizable fiscal stimulus approved in the United States and the onset of a massive global vaccination campaign, largely explains the projected increase in foreign demand growth in 2021. The resilience of the goods market in the face of global crisis and an expected normalization in international trade are additional factors. These considerations and the expected continuation of a gradual reduction of mobility restrictions abroad suggest that Colombia’s trade partners could grow on average by 5.2% in 2021 and around 3.4% in 2022. The improved prospects for global economic growth have led to an increase in current and expected oil prices. Production interruptions due to a heavy winter, reduced inventories, and increased supply restrictions instituted by producing countries have also contributed to the increase. Meanwhile, market forecasts and recent Federal Reserve pronouncements suggest that the benchmark interest rate in the U.S. will remain stable for the next two years. Nevertheless, a significant increase in public spending in the country has fostered expectations for greater growth and inflation, as well as increased uncertainty over the moment in which a normalization of monetary policy might begin. This has been reflected in an increase in long-term interest rates. In this context, emerging market economies in the region, including Colombia, have registered increases in sovereign risk premiums and long-term domestic interest rates, and a depreciation of local currencies against the dollar. Recent outbreaks of COVID-19 in several of these economies; limits on vaccine supply and the slow pace of immunization campaigns in some countries; a significant increase in public debt; and tensions between the United States and China, among other factors, all add to a high level of uncertainty surrounding interest rate spreads, external financing conditions, and the future performance of risk premiums. The impact that this environment could have on the exchange rate and on domestic financing conditions represent risks to the macroeconomic and monetary policy forecasts. Domestic financial conditions continue to favor recovery in economic activity. The transmission of reductions to the policy interest rate on credit rates has been significant. The banking portfolio continues to recover amid circumstances that have affected both the supply and demand for loans, and in which some credit risks have materialized. Preferential and ordinary commercial interest rates have fallen to a similar degree as the benchmark interest rate. As is generally the case, this transmission has come at a slower pace for consumer credit rates, and has been further delayed in the case of mortgage rates. Commercial credit levels stabilized above pre-pandemic levels in March, following an increase resulting from significant liquidity requirements for businesses in the second quarter of 2020. The consumer credit portfolio continued to recover and has now surpassed February 2020 levels, though overall growth in the portfolio remains low. At the same time, portfolio projections and default indicators have increased, and credit establishment earnings have come down. Despite this, credit disbursements continue to recover and solvency indicators remain well above regulatory minimums. 1.2 Monetary policy decision In its meetings in March and April the BDBR left the benchmark interest rate unchanged at 1.75%.

This paper firstly developed a three-dimensional (3D) finite element model (FEM) for enhanced C-channels (ECs) in steel-UHPC-steel sandwich structures (SUSSSs). The FEM was validated by 12 push-out tests on ECs with UHPC. With the validated FEM, this paper performed in-depth parametric studies on shear behaviours of ECs with ultra-high performance concrete (UHPC). These investigated parameters included bolt-hole gap (a), grade (M) and diameter (d) of bolt, core strength (fc), length of C-channel (Lc), and prestressing force ratio on bolt (ρ) in ECs. Under shear forces, the ECs in UHPC exhibited successive fractures of bolts and C-channels. Increasing the bolt-hole gap within 0-2 mm has no harm on the ultimate shear resistance, but greatly improves the slip capacity of ECs. Increasing grade and diameter of bolts improves the shear resistance and ductility of ECs through increasing the PB/PC (shear strength of bolt to that of C-channel) ratio. Increasing the core strength increased the shear resistance, but reduced the ductility of ECs due to the reduced PB/PC ratio. The ECs with Lc value of 50 mm offer the best ductility. Prestressing force acting on the bolts reduced the shear strength and ductility of ECs with UHPC. Analytical models were proposed to estimate the ultimate shear resistance and shear-slip behaviours of ECs with UHPC. The extensive validations of these models against 12 tests and 31 FEM analysis cases proved their reasonable evaluations on shear behaviours of ECs with UHPC.

Steel structures have been widely used in constructions due to their advantages of lightweight, high strength, short construction time and high recycling and reuse potential. Fracture failure in steel structures should be prevented to avoid collapse of the whole structures. Micromechanical fracture models can capture the fracture initiation mechanisms and therefore can be used to predict ductile fractures in steel. Twelve smooth round bars were carried out to obtain the material properties and 36 notched round bars were tested to calibrate the parameters of stress modified critical strain (SMCS) model and the void growth model (VGM) for structural steels (Q235B and Q345B) and the corresponding welds. Specimens were extracted from the base metal, the weld metal and the heat affected zone (HAZ) to investigate fracture behaviour in different parts of the welded joint. Scanning electron microscope (SEM) measurements were taken and finite element models were developed to calibrate the models. The test results and calibrated parameters are reported. Moreover, the calibrated models are applied to analyses the fracture behaviour of welded joints and their accuracy are validated. The calibrated and validated models can be used for further numerical fracture analysis in welded steel structures.